Arch Linux

Dear maintainer,

I noticed a warning while updating graphviz to 3.0.0-2 today:

```
(16/29) upgrading graphviz [######################] 100%
Warning: Could not load "/usr/lib/graphviz/libgvplugin_gdk.so.6" - It was found, so perhaps one of its dependents was not. Try ldd.
Warning: Could not load "/usr/lib/graphviz/libgvplugin_gtk.so.6" - It was found, so perhaps one of its dependents was not. Try ldd.
Warning: Could not load "/usr/lib/graphviz/libgvplugin_gdk.so.6" - It was found, so perhaps one of its dependents was not. Try ldd.
Warning: Could not load "/usr/lib/graphviz/libgvplugin_gtk.so.6" - It was found, so perhaps one of its dependents was not. Try ldd.
```

It appears that libgdk-x11-2.0.so.0 is missing, which belongs to the 'gtk2' package:

```
[imre@oyster ~]$ ldd /usr/lib/graphviz/libgvplugin_gdk.so.6 | grep 'not found'
libgdk-x11-2.0.so.0 => not found
[imre@oyster ~]$ pacman -F libgdk-x11-2.0.so.0
extra/gtk2 2.24.33-2
usr/lib/libgdk-x11-2.0.so.0
multilib/lib32-gtk2 2.24.33-1
usr/lib32/libgdk-x11-2.0.so.0
```

You can reproduce this by removing the 'gtk2' package from your system and reinstalling graphviz. I noticed that 'gtk2' is in the PKGBUILD's optdepends. Maybe it can be promoted to 'depends' in order to prevent this warning? Or maybe it shouldn't if the package is not absolutely necessary and you want to keep the list of dependencies as small as possible, in which case maybe the warning can be suppressed in some way. I would favor the additional dependency, but this decision is best left up to you.

Thanks for maintaining the Arch graphviz package!