shorten filename if necessary when copying from NTFS to FAT (sf.net)

When copying files from NTFS to FAT, or even from one FAT folder to another which is "deeper" in the tree, it is possible that the resulting destination filename plus path exceeds some filesystem limit. When this happens, CopyHandler just shows a general error message that the file couldn't be copied. It would be nice if the program could tell the user the reason for this error and give a possible solution: renaming the file in question (shorter filename) or moving it to a different folder instead (thus shortening the path).
(migrated from https://sourceforge.net/p/copyhandler/feature-requests/32/).