A Makefile has very exact rules about tabs beginning an action line (for
this IZ, I'm referring to an action as the lines following a line of the
form "foo.o: foo.c"). If the line begins with spaces then its syntactically
incorrect and the make will fail.

Currently, pressing return from a rule line ("foo.o: foo.c") auto-indents
a tab. But users can either overcome this by backspacing and typing spaces
or they could read in a Makefile with spaces here. 

It would be helpfull for the editor to highlight these spaces in red (its
not an original idea, vim does it and other editors may as well).