Normally a valueless symbol remains valueless and a symbol with a
value keeps having one. But just in case a symbol does get changed
from valueless to having a value, make sure there's a space between
the symbol and the value. And if a symbol gets changed from having a
value to valueless, strip trailing whitespace.
Add corresponding tests.
Also fix the case of a valueless symbol added with the set method,
which would have resulted in attempting to use None as a string. This
only happened with the Python API, not with the command line API.
Run config.py with various options and store the results in files.
This script also supports the now-removed config.pl.
This is a framework to run non-regression tests on config.py: run it
with the old version, run it with the new version, and compare the
output.
This is deliberately not a functional test suite so that we don't need
to maintain a set of known outputs. When something changes in
config.py (or config.h), run the script before, run it after, and
check manually whether any differences in the output are acceptable.
