This makes the tests also work on systems which don't run X.

See ChangeLog / man/feh.1 "--thumb-redraw" for more

Depending on --thumb-width/--thumb-height, either .thumbnails/normal or
.thumbnails/large is used. For higher dimensions, thumbnail caching is still
silently disabled, this should also be what the standard indicates.

(This was actually meant to be included in
f4420709)

Centering didn't work if the text below the thumbnail was wider than the
thumbnail itself. Fixed.

The ButtonRelease check only knew pan mode, so releasing the blur key changed
to the next image.

The menu background images were not properly free()d

Does not yet work with initial zoom value != 100%

No need to edit config.mk to set addictional CFLAGS/LDFLAGS or change the DESTDIR etc. now

This fixes imlib2 warnings (and occasional X errors/segfaults), which used to
occur when all files in feh's filelist were suddenly deleted by an external
application. Now, feh simply quits with "No more slides in show" (which makes
more sense, IMHO).

Just in case, and we don't want the compiler to complain about it, do we? ;)