Make request->tuple to be iovec
Add alloc_factor argument to obuf_create()
Add obuf_ensure() and obuf_advance() API
Replace tbuf with obuf
Merge remote-tracking branch 'origin/master' into gh-291-call-result

Conflicts:
	src/box/tuple.cc
	src/box/tuple.h
gh-291: tbuf erasure review fixes. Erase a bit more.

Fix a bug in iovec_join which would overwrite data of
the first iovec with subsequent iovecs.
Double the default buffer size.
Merge branch 'master' of github.com:tarantool/tarantool