[plt-scheme] new Windows DLL names

DrScheme v200 is distributed with three DLLs:

 libmzgc.dll
 libmzsch.dll
 libmred.dll

Until this morning, DrScheme v200.2 also used three DLLs with the same
name. Of course, they're completely incompatible with the v200 DLLs,
which is asking for trouble.

The newly exp-tagged Windows projects and makefiles in CVS create

 libmzgcxxxxxxx.dll
 libmzschxxxxxxx.dll
 libmredxxxxxxx.dll

instead. The obnoxious "xxxxxxx" is a placeholder for a version number.

For local development, you can continue building and using
MzScheme/MrEd/DrScheme as before, but with the new names (i.e., use the
"xxxxxxx" DLLs directly).


For the final distribution of a version, we'll replace "xxxxxxx" with a
specific version number. Only version-named DLLs will be installed into
the system directory, which means that multiple versions of DrScheme
can be installed on the same machine, and none of them will be confused
with the "xxxxxxx" intermediate DLLs of CVS-based builds.


In case someone needs version-specific DLLs between final releases, the
"winvers.ss" program in the "setup" collection installs the version
number. See plt/src/worksp/README for more information, but the short
story is that running

    mzscheme -mvqL winvers.ss setup

currently changes the DLL names to

 libmzgc200.2_0.dll
 libmzsch200.2_0.dll
 libmred200.2_0.dll

and patches mzscheme.exe, mred.exe, and mzcom.exe to refer to the new
names.

Matthew