Extend to expect comma separated modules names

In order to compress the length of the module map we change from:

    name=location:name=location...

Where if there are multiple names at the same location you need multiple
entries with the same location, to:

	name[,name[,name]]=location:name[,name]=location
PYTHONPATH -> PYTHONMAP helper

We add the first draft of a command to output a module map as expected
by porter for the current environment. It looks at the sys.path and
attempts to dump out a map for all the modules found on it.