Rename range->min_key to range->begin, as it actually denotes not the
minimal key across all entries in the range, but the lower bound of the
range, and introduce range->end for the upper bound of the range.
For adjacent ranges left->end == right->begin. If a range is leftmost,
then range->begin == NULL. If a range is rightmost, then range->end ==
NULL. Store range->{begin,end} in range file on checkpoint and load them
on recovery.

This is required by the following patch to check that ranges do not
intersect.

All we need to initialize range->path is range->id and index->path. Both
are known at the time of range allocation and never change. So let's do
range->path initialization right in vy_range_new() instead of postponing
it until range recovery/write.

It is uninitialized in case of error injection.

Closes #1755

We have env->indexes list. No need to store all indexes in an array in
addition to that. Note, I move rlist_add adding a new index to the
env->indexes list from vy_index_new() to vy_index_open() so that it only
becomes visible to the scheduler after having been successfully loaded.
This change does not make any difference apart from that.

All manipulations on index->refs, which ref_lock is supposed to protect,
are done from the tx thread, so the lock is not needed.

Move the miniature truncate test to gh.test.lua and remove disabled
test file.

Rename connection option 'legacy_call' to 'call_16'.
If you live long enough you know that even shiniest and brightiest
call's time may come.

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