Follow-up to r38120: Add a workaround for lazy users of Expat.
Follow-up to r38120:
Add a workaround for lazy users of Expat.

[ Reverted in r38164. ]

* configure.ac
  (Expat): Use libraries printed by `apu-1-config --libs` when Expat wasn't
   found in standard location or location specified in argument of --with-expat
   option.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion