* Add add'l output formats for graphviz
Add support for additional output formats to graphviz, including gif,
jpg, pdf, and png.
Graphviz calls its pango+cairo option *pangocairo* so I followed suit.
Libgd was missing jpeg/jpg support. None of the other supported
formats are conditionalized and there is no --with/--without support,
so I followed suit.
* Fix ghostscript plugin
When I installed thusly:
spack install graphviz+pangocairo+libgd^cairo+X^pango+X
the ghostscript plugin tripped over some variable names that had
changes in `gs@9.18:`. This fixes them.
* Remove wayward import of tty
aa51e766cd