(Crash on rename index).

Do not invalidate a reference to key_def in alter space,
when preserving the old index.

Instead, update the old key def with new parameters.

See #347

See #347

Conflicts:
	doc/www-data.in/download.cmake

Conflicts:
	cmake/rpm.cmake
	extra/rpm/tarantool-scl.rpm.spec
	extra/rpm/tarantool.rpm.spec.in

Add provisioning for user type.
Support user type in alter.
Do not return roles in user_by_name().
Make it possible to grant privileges on roles ('execute').

 * remove vclock_merge
 * remove vclock_destroy
 * use `server` instead of `node`
 * use `signature` instead of `lsnsum`
 * refactor vclock_from_string code