Enabled dbug macros

* wsrep_provider_options dbug and signal can now be used to control
  DBUG package controls
* Added new macro GU_DBUG_SYNC_WAIT in gu_debug_sync.hpp for easy
  sync point definition
* Added several sync points in replicator
Read revision number from file if not given
Strip newline from revision
Merge branch '3.x' of https://github.com/codership/galera into 3.x
Init CFLAGS/CXXFLAGS from environment