Renumerate IPROTO error codes

This patch changes iproto codes enumeration scheme:

* 0 - OK (indicates success result of DML or ADMIN commands)
* [    1, 1<<14) - DML & ADMIN commands
* [1<<14, 1<<15) - recoverable errors (e.g. memory issue)
* [1<<15, 1<<16) - unrecoverable errors (e.g. duplicate key)
Renumerate IPROTO error codes

This patch changes iproto codes enumeration scheme:

* 0 - OK (indicates success result of DML or ADMIN commands)
* [    1, 128) - DML & ADMIN commands
* [32768, 65535) - errors (1<< 15 | ER_XXX from errcode.h)

Other ranges are reserved for future use.
fix GH-377 bps_tree test
Merge branch 'master' of https://github.com/tarantool/tarantool
gh-310: multi-statement transactions in absence of yield

Implement transactions infrastructure for autocommit mode.
Prepare txn.cc for multi-statement transactions.
Merge branch 'master' of github.com:tarantool/tarantool
Merge remote-tracking branch 'origin/gh-344-iproto-error-codes'
Merge branch 'gh-344-iproto-error-codes-v2'

Conflicts:
	src/box/replica.cc
	src/box/txn.cc
	src/iproto_constants.cc
	src/iproto_constants.h
	test/box/bad_trigger.result
	test/box/call.result
	test/lib/tarantool-python
Update tarantool-python
Remove padding from IPROTO fixheader
Fix #356: rename admin_port to admin, primary_port to listen
Rename port_uri to uri
Merge branch 'master' of https://github.com/tarantool/tarantool