Problems with tests

[lexurco]

Hello,

I was trying to make a port of u2ps, and ran into some problems with tests:

• The *.c tests seem to be straightforward enough -- just {,g}make
  them and execute.
• I don't quite understand how the *.ps tests are supposed to work.
  Do I need to invoke gs with some specific arguments, or
  environment to run these?
• The *.sh tests seem to be failing for me, but that's probably due to
  the way gs is compiled on my system. I did, however, notice a bashism
  on the line 10 of px_reduce_rgl.sh: ">&/dev/null". Would you consider
  instead making it ">/dev/null 2>&1"?

Would you please consider writing a bit of documentation for the tests
(like a few comments should be enough), and writing a make target to
run them automatically?