v8cgi: use optional deps
Move MD5 deprecation warning into Pathname#md5

This way it will print when the verification takes place, making it a
bit more obvious which formula it refers to.
cdo: fix dep
libnids: fix deps
tokyo-tyrant: fix dep
weechat: fix deps
htmlcompressor: fix deps
zint: fix dep
vtk: fix dep
rrdtool: fix dep
graphicsmagick: fix deps