* Fixed a bug that caused all but the first stackframe walk to fail with an error.
* Improved thread safety of stack walking.
DevNotes: When walking stackframes multiple times from the same process, only the first stackframe walk would work and all others would fail with an error because of calling SymInitialize multiple times. So now SymInitialize is only called once and SymRefreshModuleList is used prior to walking, if available. (only available in winDbgHlp.dll v6.5 or later)
git-svn-id: http://pcsx2.googlecode.com/svn/trunk@3546 96395faa-99c1-11dd-bbfe-3dabce05a288