Permit %verifyscript from non-installed packages

Permit %verifyscript from non-installed packages
- Verification from non-installed packages can be useful sometimes:
  http://lists.rpm.org/pipermail/rpm-maint/2011-May/003015.html
- %verifyscript is unlike all other scriptlets so might as well
  take some shortcuts and bypass rpmteProcess() & all, just
  create a lone rpmte, force the header we got and call rpmpsmRun()
  directly on it, bypassing rpmteProcess() which is only an
  unnecessary complication here (based on patch by Michael Schroeder)