#638, checking/configuring in cmake pthread_yield and sched_yield; READLINE_ROOT for better readline control;
On ARM chars are unsigned

This code didn't worked on ARM, changing the table and parameters to int seems to work fine on any platform.
Merge pull request #641 from mingodad/patch-1

On ARM chars are unsigned
Update faq.rst
When dropping a role, revoke that role from whoever it was granted to first.
Merge branch 'master' of github.com:tarantool/tarantool
Implement a grant of a privilege to a role.

Introduce 'public' role.
Auto-grant 'public' to every user.
Update the snapshot.
#638, minor fixes & updates;
Darwin fixes: code review.
Merge branch 'darwin-support'
Merge branch 'master' of https://github.com/tarantool/tarantool