gh-727: memtx proper rollback in case of out of memory, add comments
gh-727: memtx proper rollback in case of out of memory, add comments

vasilenkomike/tarantool,condor-the-bird/tarantool,vasilenkomike/tarantool,rtsisyk/tarantool,KlonD90/tarantool,guard163/tarantool,ocelot-inc/tarantool,mejedi/tarantool,dkorolev/tarantool,guard163/tarantool,ocelot-inc/tarantool,rtsisyk/tarantool,ocelot-inc/tarantool,vasilenkomike/tarantool,dkorolev/tarantool,KlonD90/tarantool,KlonD90/tarantool,mejedi/tarantool,guard163/tarantool,KlonD90/tarantool,Sannis/tarantool,Sannis/tarantool,Sannis/tarantool,dkorolev/tarantool,Sannis/tarantool,KlonD90/tarantool,rtsisyk/tarantool,dkorolev/tarantool,vasilenkomike/tarantool,guard163/tarantool,condor-the-bird/tarantool,dkorolev/tarantool,condor-the-bird/tarantool,rtsisyk/tarantool,mejedi/tarantool,mejedi/tarantool,vasilenkomike/tarantool,ocelot-inc/tarantool,condor-the-bird/tarantool,Sannis/tarantool,condor-the-bird/tarantool,guard163/tarantool