(FileOpContextUI): rename labels for files.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Use vfs_path_as_str() to get string representation of tree_entry::name.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Add DIR_IS_DOT and DIR_IS_DOTDOT macros

...to detect "." and ".." directories, respectively.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>