Fix pager bug #25!

Finally fixed! An extra check to see whether the pager is at the
bottom. Apparently if you click to put the cursor somewhere that's
not the end of the text buffer, then scroll up with your scroll
wheel, then _sometimes_ the pager wouldn't stop paging when you
paged down to the end again, because the GtkAdjustment's "changed"
signal didn't fire. But now that's fixed.

Conflicts:
	libchimara/pager.c