thumbnails: avoid crash with jp2 images
When thumbnailing a directory with jp2 some times nautilus was crashing. However tests on gdk_pixbuf were successful and gnome-desktop-thumbnails generation tests were also working. Also, nautilus is using raw pthreads in the thumbnail generation code, and seems the crash was actually only happening when inside the pthread and when using gdk-pixbuf, not only the gnome-desktop-thumbnail. Looking at the implementation of glib in threads and nautilus, one of the differences is that nautilus sets a stack size. The crash is happening because, unluckely, libjasper with some big images is using more stack size than the one nautilus is setting, which leads to a crash in libjasper. To fix it, remove the stack size set by nautilus, similarly to what glib does, not setting an actual stack size. Obviously the right thing to do is rewrite nautilus code to use the glib threads, but I want to let that as a newcomer bug to do.