For issue #3301 ("Cannot build without OpenSSL"), add some (hopefully) helpful info to 'configure --help' output.
For issue #3301 ("Cannot build without OpenSSL"), add some (hopefully)
helpful info to 'configure --help' output.

* configure.ac
  Add --help information about the --with-openssl parameter, which
  (like --with-ssl) isn't used by Subversion itself, but by a
  dependent library (Serf, in this case).  Also note the alternatives
  available (Serf for Neon, and vice-versa).

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