This changes the behaviour of "feh --start-at FILENAME" as follows:

Previously, this would cause feh to load all files in the current
working directory, since no files or filelists were specified on the command
line.

Now this is a special case: feh will extract the directory component from
FILENAME, load all files in that directory, and display FILENAME.
This way, it's possible to use "feh --start-at ~%f" in XDG Desktop files
and browse files in feh using the prev/next keys

Closes #372
Closes #420

This more closely resembles the expected behaviour of --start-at, but
may lead to mismatches if several files in the filelist have the same
basename.

Closes #206

Related to #372 and #420

This is in line with other software. save_filelist now defaults to "L".

Quoting glibc rand(3):

The  versions  of rand() and srand() in the Linux C Library use the same random
number generator as random(3) and srandom(3), so the lower-order bits should be
as  random  as  the  higher-order bits.   However,  on  older  rand()
implementations, and on current implementations on different systems, the
lower-order bits are much less random than the higher-order bits.  Do not use
this function in applications intended to be portable when good randomness is
needed.  (Use random(3) instead.)

Closes: #124

Partial fix of: #310

Fixes: #415

Trying to handle stdin when select() in fact returned an error due to being
interrupted by a signal is a rather bad idea.

See issue #405

See issue #405

See issue #405

Closes #400

Closes #279

Addresses part of issue #75