Update Android port

Update Android port

* etc/PROBLEMS: Document problem with default monospace font.
* src/fileio.c (check_mutable_filename): Check /content as well.
(Fcopy_file, Fdelete_directory_internal, Fdelete_file)
(Frename_file, Fadd_name_to_file, Fmake_symbolic_link)
(Fset_file_modes, Fset_file_times, Ffile_newer_than_file_p)
(write_region): Adjust accordingly.
(Fset_visited_file_modtime): Remove unnecessary restriction.
* src/filelock.c (make_lock_file_name): Don't interlock files
under /assets and /content.
* src/inotify.c (Finotify_add_watch): Fix typo.