Revert the last two commits

This solution did not work. I'll have to think of something more
elaborate.
bostree: Upstream update

Introduces new features required for solving bug #23
Globally lock the file structures for unique access

Whenever a file is somehow altered or needs to be accessed consistently
over multiple lines of code, lock a mutex. I've tried to avoid this, but
it seems that every other solution can be lured into a race condition.
Display help if the user doesn't provide any images to load.
Exit with success if the help was displayed

Related to pull request #22.

Other programs exit with status 0 if invoked without parameters / when
the help is shown. pqiv still returns 1 if all images failed to load,
which is the case a scripts couldn't test for on its own, so I think
that's okay to do the same and return 0.
Updated README with latest change
Clear current_file_node if it is unloaded and there are no other images

Without this change, pqiv -lr crashed when the first few lines were not
actually images. It called next_file() without a valid
current_file_node(), because it thought that current_file_node was set
(when it was actually removed).
Accept floating point slideshow intervals
Removed memory allocation failure warnings

glib calls abort() whenever a memory allocation fails, so this code was
useless. See http://www.gtk.org/api/2.6/glib/glib-Memory-Allocation.html
Update the info text if new images are found (either via --watch-directories or --lazy-load)

Furthermore, the region of the window where the info text is visible is
repainted. The region is estimated by the last known bounding box plus
some additional pixels to the right. This is a compromise to keep the
overhead low.

See bug #19.
Show the cursor in fullscreen while the jump dialog is open
Fixed call to initialize_gui()
Added --max-depth

Suggestion for a --max-depth feature like the one find(1) has. See
bug #24 for the related discussion.
Added --browse

See bug #25. qiv had this option for some time now, and with --max-depth
this is actually useful if pqiv is used as a handler for images in a
file manager, where users expect to be able to switch between images
from the same directory.

(Note: This does work with --sort and --shuffle. The first parameter is
 still the first image displayed. ☺)
Merge branch 'master' into redraw