#41 Win32: use %HOME% if set

[Michael Schumacher]

When creating the .filmgimp (or .cinepaint, assuming
that it will be renamed, too) directory, CinePaint
should use the HOME environment variable if it is set.

Maybe another environment variable could be added,
CINEPAINT_DIRECTORY, if HOME isn't the right place but
can't be changed for some reason.

On WinNT systems, a concatenation of HOMEDRIVE and
HOMEPATH could be used if CINEPAINT_DIRECTORY or HOME
aren't set.

If there is no way to determine a user specific
directory, then the current behaviour (directory <user
name> in CinePaint programs path) could be used.