Add Variant "+http2" to the apache2 port

[alphanull (alphanull)]

I need to run my local webserver with http2 enabled for developing and testing. However, there is currently no built in support for this package. So I am forced to manually recompile apache with a modified port file after each update, which is quite cumbersome!

But actually I think the changes won't be that complicated - I am no expert with portfiles, but something similar like this should do it:

variant http2 description {Enable HTTP/2 support} {
    depends_lib-append port:nghttp2
    configure.args-append --enable-http2
     configure.args-append --with-nghttp2=/opt/local/lib/libnghttp2.14.dylib \
}