client: Make aggregated to handle empty sequence

If begin == end (input sequence is empty) call to result complete
with -ENXIO and "has no requests to send" error
Core: Missed error notification added
Merge pull request #366 from euroelessar/aggregated_fix

client: Make aggregated to handle empty sequence
Merge pull request #367 from IIoTeP9HuY/master

Core: Missed error notification added
Merge branch 'master' of https://github.com/IIoTeP9HuY/elliptics into io_stats
Cache: Time stats usage example updated
Cache: time_stats are now header only
client: Added capped collections
Merge pull request #368 from euroelessar/capped

client: Added capped collections
React added as submodule
Cache: react namespace updated
core: added socket close debug
reconnect: fixed groups array allocation. limit group array for random selection by 4096 groups
Merge branch 'master' of github.com:reverbrain/elliptics

Conflicts:
	library/trans.c
v2.25.1.0
indexes: there is no nullptr on older compilers
test: added server library to test-common itself, since it uses them
cache: define _GLIBCXX_USE_NANOSLEEP to enable sleep_for()
tests: added missing header
Cache: Cache destruction monitoring added