feature: test and pytest use command-line arguments
feature: test and pytest use command-line arguments

I found myself switching between 'make test' and py.test for individual
file tests.  This way I can use the py.test command line arguments on
the make file so there are no new commands to remember.

Use the output of install as the file flag.  Now I get to keep the
install for reference.

Cleaned up and made some of the variable a bit more readable.

jidn/python-Makefile