As for as stopping on error: apm_packages_full_instal (in apm-install-procs.tcl) catches the error. Re-throwing it would stop it.
Strangely enough, I did get it to work on 7.1.2 on Windows machine. I've re-installed latest 7.1.2 RPMS from postgresql.org but still have the same issue on RH 6.2.