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.

Track granted roles.
Represent roles granted to a user with a bitmap.
Disallow loops in role grants.
Add tests for box.schema.user.grant('username', 'rolename')
Add basic tests for loops in grant sequences.

Rewrite largely buggy code in authentication token lookup.
Do not waste space on authentication token bitmap, correctly
check for overflow of the bitmap.

A few renames.

Rewritten

Write a function which can be used to check whether a user
exists or not.

Fixes gh-632.

Users should be able to specify some flags in CC or CXX variables
instead of putting it to to C/CXXFLAGS (e.g. CC="cc --sysroot=xx -m32").
We faced with this problem on Intel Edison/Galileo SDK.

added comments to rtree, added more misc tests for rtree, moved key validation from index to key_def, added NUMBER key type