- Skip leading forward slashes when setting the temp directory.
- Add a utility function to set the temporary directory
which is used for the user preferences & environment variables.
This issue was raised by #95411 where "//" resolves to "/",
then asserts when passed to Blender's file-system functions.
However the crash referenced in this report looks to be caused
by Collada failing to write to the temporary directory which
can be handled separately.
Ref !118872
Campbell Barton
c19cdc343f