Support --with and --without options for libsodium and pgm

The configure script treated the --without-libsodium and --without-pgm options the same as --with-libsodium and --with-pgm.  Change 64a92cce49534c0b4e337e0aad3ebb95eddbfdb8 uses $withval instead of "yes" if a --with option is specified to handle this case.

The rpm spec unconditionally passed --with-pgm, but did not add build or runtime dependencies for openpgm.  Change 9078a7a4a59698b9bd50d547bc1d084b70fd4d7e adds support for specifying --with pgm or --without pgm on the rpmbuild command line, and ensures dependencies are added to the rpm if needed.  I added the same support for libsodium at the same time, as that's a similar configure-time option.  I'm not quite sure the --with-pic and --with-gnu-ld options were passed for x86 systems, so I left them be.  However, I made it possible to override them with --without pic and --without gnu-ld on the rpmbuild command line.  There was also a perl and python dependency for x86 systems, but doesn't make any sense at all, so I removed that.

If these changes are accepted, I plan to prepare the second for pull up to zeromq4-1.  Since the first is atop recent work by @pmienk, it may be best for him to be involved.