add rpm packages for PostgreSQL and MySQL.
do not directly require mysql-devel and postgresql-devel
packages.
Rewrite tuple[x] and #tuple bindings using FFI
tuple[x] FFI bindings - minor changes

Do not return extra result from tuple:__index method.
tuple:pairs and tuple:next FFI bindings
Remove debug message from tuple_iterator_next
Temporary changes
Fix tests after merging tuple-methods-ffi

Minor changes - fix msgpack.decode for zero-size arrays and update
line numbers in result files.
Reimplement iterators using FFI

This patch replaces Lua/C bindings to iterator by FFI.
Optimize index functions for FFI iterator
Merge branch 'stable'
update pg and mysql module install prefix
update sophia submodule
Merge branch 'stable'
Merge branch 'master' of https://github.com/tarantool/tarantool