[patch] graphics/librsvg2: restore broken scaling in rsvg-convert(1)

[Alexey Dokuchaev]

Hi gnomers,

We currently have librsvg2 2.40.13 in ports, which contains very annoying
bug (non-working scaling) in rsvg-convert(1):

    https://bugzilla.gnome.org/show_bug.cgi?id=520654
    https://bugzilla.gnome.org/show_bug.cgi?id=762115

This regression was apparently fixed in recent versions, but unless update
to 2.40.16 is imminent, I'd like to add and commit this patch to the port:

    https://people.freebsd.org/~danfe/patch-revert-bgo-520654-support-export-id-in-rsvg-convert

./danfe