Modernize, reformat, and simplify this port.

User-facing changes, some of which required a PORTREVISION bump:

• Explicitly depend upon libgpg-error.so
• Just depend on readline for everybody, rather that silently linking against it on 10.x and when certain knobs were enabled
• Don't download the .sig file
• Install manpages for everybody. As a side effect, everybody gets the info files. Also, put the help docs into DOCSDIR, not DATADIR. AFAICT, they weren't called from gpg itself
• Reword the pkg-descr and COMMENT
• Fold the pkg-install into pkg-plist, and loosen the semantics for creating the gpg symlink, and tighten those for removing it
• Remove the pkg-message. The pinentry port installs a dialogue