Allow relative paths in Copy and Move dialogs consistenly
To prevent mistakes
./relative/path/to/[...] (note the necessary dot) could perhaps be required instead of
relative/path/to/[...].
../relative/path/to/[...] (ancestor paths) should be supported too.
At the moment (1.53.4) strang things happen with relative paths:
Typing a path without any '/':
1. one can copy a file to a non-existing file (even from the Move popup!)
2. one can copy directories into existing directories (alas even from the Move popup!)
3. one can copy directories to non-existing directories (alas even from the Move popup!)
Using relative paths with at least one '/' seems to do absolutely nothing in all other cases I could test.