* First, try to load the file from the given filename. This is either absolute or relative to the current .blend
* If file is found using the given filename directly then look for the file in the datafiles/brushicons directory (local, user, or system).
* Note: This commit does not update the .blend to reference the default icons
* Note: This commit does not make sure that the build system copies the default icons to the 2.52/datafiles/brushicons directory