[Distutils] MSVC7 directories

[Mark Hammond]

> If I understand Mark correctly, the MSVC 7 GUI doesn't pick up the
> enviroment vars itself - this is (one of?) the difficultiy I see.

Nope, this isn't a problem.  I have 2 specific problems:

* Manually setting LIB/INCLUDE has no effect, as distutils overwrites these
values with what it thinks they should be
* MSVC7 doesn't seem to store its paths in the registry.

MSVC7's GUI probably doesn't pick up the LIB/INCLUDE vars at startup time -
but this is rarely an issue - the only time I expect to set or use these
vars is when running from the command-line (which is exactly where distutils
is run from :)

I think there is a simple fix to keep most people happy.  distutils can just
*append* the existing env var value to the new value.  I think it is
acceptable to say distutils wont let you set these to change the location of
standard libraries or headers, but will let you add new ones.

Mark.