Fix gh-799 net.box: use a single watcher
Fix gh-800 net.box: remove reconnect fiber
Fix gh-1138 net.box: an active connection is never garbage collected
Fix gh-1750 net.box: hangs after reconnect

  * Net.box() connection refuses to work with 'Lua console';
  * console method in net.box dropped (TBD: docs;)
  * internals changed, code depending on internals WILL break;
  * different state chart, see comments in source code (TBD: docs;)
  * new option: legacy_call to request call 1.6 semantics;
  * extension: option wait_connected treated as timeout if T == number;
  * wait_connected() return true/false as docs say;
  * wait_state() moved to public API (TBD: docs.)

Replace internal methods with public ones when possible.
Remove redundant calls.
Remove console tests - console support in net.box is being phased out.

Rename tests, reduce sleep interval, cleanup after the test a bit
more thoroughly, disable the test in release mode.

Error was with modifying primary key. In following case:
   upsert lsn=10, modify primary key
   upsert lsn=9,
   replace lsn=8
vy_apply_upsert returned replace,lsn=9, but answer must be
   upsert lsn=9 merge with replace lsn=8

At some point we (I) decided to implement transaction-level
DDL-DML dependency tracking, and removed index reference counting
from vinyl. Unfortunately we failed to implement this quickly.

Put the reference counting back for now.

This prevents index destruction while there is an open cursor using it.
Fixes the sporadic crash of options.test.lua

To build on older linux distributions, like Debian Wheezy,
the target_include_directories should be replaced with
include_directories.

A breakthrough technology made possible thanks to the latest
research from British scientists.
Remove srzone and move compact_wm to vy_conf.

The zone map has been made obsolete by the priority queue
sorted by run count.

Don't forget to set an error in the area upon a library error
or out of memory.

* Use coeio in TX thread for disk reads
* Add range_version and range_index_version checks to vy_read_iterator
* Rework vy_read_iterator to re-create vy_merge_iterator on
  invalidation

Fixes #1756

* Reduce tuple size to meet box.cfg.vinyl.page_size value
  Cover cases when page contains more than one tuple.
* Reduce test time from 200 seconds to 20.
  200 seconds was too large and generated more than 20 GB
  of data on my machine

* simplify rollback loop
* add comments
* extract xlog_tx constructor/destructor logic into functions
* remoe xlog_tx_write() from xlog_close(): don't attempt to
write uncommitted transactions at shutdown

Currently, we name range index file by the lsn from the time of the last
checkpoint. As a result, each time we checkpoint an index we have to
relink its range index file. Actually, all we want to achieve here is to
have different range index files for different reincarnations of the
same index. This can be done in an easier way - we can just name range
index file by the lsn of the index creation, which was added to key_opts
by the previous patch. This way we don't have to rename any files.

It can be useful for naming on-disk data in case of vinyl. The next
patch will use it to simplify range index naming.

 - check read() result carefully
 - fix buf memory leak
 - fix run memory leak in case of read error

* Merge vy_run_read_page to vy_run_iterator_load_page
* Move struct vy_page code to struct vy_run_iterator section

Needed for #1756

Change default value of box.cfg.vinyl.threads to 1.
Keep 3 workers in the test suite.

Wake up scheduler if range dump conditions are met.

Fixes #1769

Refactor replication relay to invoke Engine::join() using TX thread.
Now engines can start their own threads when needed:

* MemTX starts a new cord to read rows from a snapshot file.
* Vinyl should use coeio for disk operations (see #1756).

This patch fixes race conditions between relay and TX threads
for both engines.

Closes #1757

 1. Consolidate temp file creation, initial run write, and range file
    rename in a single function, vy_range_write_run(). Use it in both
    dump and compact procedures.

 2. Do unlink on range file write failure in vy_range_write_run()
    instead of postponing it unilt vy_range_delete().

 3. #2 allows us to move range->id initialization from
    vy_range_complete() to vy_range_new(), as uninitialized ->id was
    only used to check if a range file is incomplete and delete it in
    vy_range_delete().

 4. #3 allows to make index->range_id_max non-atomic, as vy_range_new()
    is only called from the tx thread (in contrast to vy_range_complete,
    which hosted range->id allocation before).

* update comments
* reduce the number of forced checkpoints

Always check return code from next_key()/next_lsn()/get().