Rearrange handling of -L linker options so that they are always before all

the -l options.  (This was not the case when using the  OpenSSL or Kerberos
options.)  Also make sure that shared library links get to see all the -L
options.  Get Kerberos 5 support to compile on Redhat 7.0.  Add OpenSSL and
-lsocket (if used/found) to libpq link.