Don't leak subtree when /usr/lib/rpm doesn't exist.
Fix 64bit problem when int != gsize to printf.
 Allow sequence REFSPECs for version/list.

 API probably needs to move to ostree library. Allows us to get a "list"
of REFSPECs, Eg.

"<newest>..<oldest>"

...as a REFSPEC will turn into a list of all the commits, inclusive.