[plt-scheme] Installing PLT as non-admin on windows

The PLT installer currently tries to write a few DLLs to the
windows\system32 directory.  This means you can't install PLT on
windows unless you're admin.  Do these dlls have to be in system32, or
is this just a convenience thing?  Seems like they could go with the
rest of the PLT executable files and an entry made in the user's PATH
(or system path if the installer runs as admin) if required.

C:\WINNT\system32\libeay32299_018.dll
C:\WINNT\system32\libmred299_018.dll