A part of #863

A part of #863

Implement box.once().

Right now there is a race in box.once(), this is somethign we'll
need to fix when we have master election on simultaneous bootstrap.

The patch merely "establishes" the syntax which is going to work
most of the time.

Don't log exceptions of dead joinable fibers - it will
be logged by the caller, so avoid double logging.

recover_remaining_wals() is now more like an iterator,
vclockset_match() is only called when there is no current WAL.

Add a test case for gaps in LSNs.

Add a directory watcher, in addition to the file watcher.

Chagne wal_dir_rescan_delay default value to 2, since now it's
merely a backup.

Fix a crash in rollbackStatement() when rolling back a
statement trying to access a non-exissting space.

space_cache_find() is called before txn_begin_stmt(), thus
there is no statement object, nothing to roll back.

Remove iditioc tests from the suite.

Change the logic of recovery_finalize() to open
the next xlog if the last xlog had zero rows.
Add a test case.

Remove recovery->finalize, use recovery->writer instead.

Hard-code 1-based error message for now, we'll use field names
in the future anyway.

Remove trailing spaces, fix typos.

Old sql code completly reomoved from tests
box/sql.test, big.sql.test refactoring
sql.tests enabled in big and box suites
Replication tests sql refactoring
parallel call.test sql refactoring
box.error test fixed in call.test

After review fixes:
1. rename remote to iproto
2. remove old sql tests
3. update test-run

*) Splitted rlist initializer to RLIST_HEAD_INITIALIZER(..) and RTREE_LINK_INITIALIZER

*) Additionally added GT iterator
*) Added  test for that

* Added a test that acts as expirationd

This patch doesn't fix the bug itself, but simplifies matters
so that there is no more .inprogress xlog files.

.inprogress xlog files were created to start automatically
from a state when the server crashed with an empty
xlog, and couldn't create a new xlog since a file with the
same LSN in the name already existed. To solve this problem,
simply bump LSN at start if the last file in the recovery
list had zero records in it.

Emtpy xlog files still lead to panic if panic_on_wal_error=true
during recovery.

Add a fix and a test case.
Propagate master error to the replica.
The replica no longer enters into an infinite loop, but stops
with a correct status in this case.

*) corrected light and bps_tree corresponingly

Use a bitmap to represent existing servers.