#1184 TCLDIR needs backslashes

[Vince Darley]

If I do 'nmake winhelp' with 'TCLDIR=../../tcl8.4'
then a 'copy' syntax error is reported. One has to
use backslashes (TCLDIR=..\..\tcl8.4). No other make
operations seem to require backslashes, so it seems
this restriction ought to be removed.

[David Gravereaux]

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user_id=7549

Fixed. I couldn't reproduce the error here, but made sure
TCLDIR was filtered. Added the same logic to INSTALLDIR,
too.