Merge pull request #1217 from johntconklin/master

Append to libzmq_la_CPPFLAGS and libzmq_la_LIBADD.
Update travis script to configure with libsodium.
Merge pull request #1218 from johntconklin/master

Support --with and --without options for libsodium and pgm
Merge pull request #1219 from pmienk/master

Update travis script to configure with libsodium.