Implement a version of create_directories that was declared, but never
defined.
UI: Fix paths when loading a trace file
* Calculation of relative paths was incorrect when a trace file was loaded for the first time and a session had to be created.
UI: Clean up trace and session loading
* Trace files are now loaded first, followed by any additional session data.
* Failing to load session data no longer prevents the trace file from loading.
In Windows, GL function pointers should be queried after the current context changes.
* Re-query the func pointers when the replayer is restoring a contxt and has made it current.
* Fixes a crash in Windows where glBindVertexArray was NULL due to out-of-date func pointers.
Merge pull request #75 from vMcJohn/master

Numerous windows fixes