GIF library changed from libungif to giflib

[Matthias Drochner <M.Drochner%fz-juelich.de@localhost>]

Hi -
since the patent concerns regarding the GIF image format are not
valid anymore I've changed pkgsrc to use "giflib" (which is
a full implementation, as opposed to "libungif"). The two
libraries can't coexist, this means rebuilding of all pkgs
using libungif.
If you don't want this right now for some reason, you can set the
make variable "GIFLIB_IMPLEMENTATION" to "libungif" which makes
the pkgs to use libungif as before.

best regards
Matthias



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