- 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
c19cdc343f