Issue #532 -  Changes to address `FastMutex` being non-recursive on Win32 platforms

Added c'tor to `Mutex` to specify if it should be recursive or non-recursive, this required:

* Minor changes to POSIX and VX implementations of `MutexImpl`
* Adding a boolean to Win32 and WinCE implementations of `MutexImpl` to indicate whether they should behave recursively or non-recursively, and a lock count for determining if the lock has gone recursive

Explicitly implemented Win32 `FastMutexImpl` as a simple wrapper around a Critical Section.

Updated `FastMutex` documentation to indicate it may be recursive or non-recursive.

Added tests for checking recursive behavior of `Mutex`.