* FEATURE: null_mutex can now be set through mwc.pl -features to use an ACE_Null_Mutex instead of an ACE_Recursive_Thread_Mutex. This is only useful if you know you will be using MADARA in single threaded applications without a transport or if you are creating your own custom transport that will enforce its own threading consistency.
* Updated various internal classes to use the MADARA_LOCK_TYPE rather than explicit ACE_Recursive_Thread_Mutex.
* Updated version to 1.9.21

git-svn-id: http://madara.googlecode.com/svn/trunk@1461 2850746a-f1c8-11dd-b507-8b4ecd5210be