We did not preload when SORT_MTIME, so check opt.sort > SORT_MTIME
before offering to sort by file size.

The CB_* enum block was run through s/, /,\n\t/g for legibility.

previously, a button/key definition with an invalid action name would assign
the specified key to the most recent valid action. E.g. "zoom_in 4\ninvalid 5"
wuold assign button 5 to zoom_in.

src/main.c: switch spaces to tabs to clobber GCC warning

The if statements are needed because we cannot pass a NULL pointer to
XFree.

src/feh_png.c: close file upon error

Add description of option "--no-recursive" to man page.

Purpose of "--no-recursive" option is disabling effect of "--recursive" option that enabled by user's theme.