abipkgdiff: Avoid uncertainty when sorting worker tasks

abipkgdiff: Avoid uncertainty when sorting worker tasks

Worker tasks that have compared the binaries of two packages are
sorted according to the sizes of the binaries they compared.  The
tasks that compared bigger binaries come first.  So the output of
these tasks is always sorted the same.

When two tasks have sorted binaries of the same size, let's sort them
by taking into account the lexicographic order of the binaries names.

	* elf_size_is_greater: Take the name of the binaries into account
	when their size is equal.  Also, assert that all comparison tasks
	have compared binaries.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>