Bug#751098: Bad "Requires:" field in the pkg-config file

[Julien Puydt]

Package: libpolybori-dev
Version: 0.8.3-3

After installing the package:
$ pkg-config polybori-0.8 --cflags
Package gd was not found in the pkg-config search path.
Perhaps you should add the directory containing `gd.pc'
to the PKG_CONFIG_PATH environment variable
Package 'gd', required by 'polybori-0.8', not found

And in fact, the Requires: in the polybori-0.8.pc file should list gdlib 
and libpng, and not gd and png. Likewise for polybori-groebner-0.8.pc.

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