Bug 20670 - abipkgdiff aborts if $XDG_CACHE_HOME does not exist
    
    This patch creates $XDG_CACHE_HOME if it doesn't exist, rather than
    just aborting.
    
    	* tools/abipkgdiff.cc (package::extracted_packages_parent_dir):
    	Ensure that the cache directory is created, even when
    	XDG_CACHE_HOME is set.  Also, remove the now useless "using
    	abigail::tools_utils::get_random_number_as_string" statement.
    
    Signed-off-by: Dodji Seketeli <dodji@redhat.com>