Larger heap for the MS-Windows build

[Eli Zaretskii]

I committed to the emacs-23 branch a change that allows Emacs to have
up to 2GB of heap space (if the OS has enough virtual memory).
Previously, only about 435MB would be available, even on machines with
a lot of memory.  This is actually due to a bug: the function that
asks Windows to reserve heap was not update after Emacs switched to
the USE_LSB_TAG configuration, and so was still trying to avoid using
pointers beyond 512MB (because the Lisp tags were once using the high
bits).

This change will be soon on the trunk as well, when it is merged from
the branch.

Please report any abnormalities you spot in memory usage.  If you
happen to need to visit large files, by all means do and see if
everything works as expected.  (You should be able to visit files up
to 512MB with the Windows build of Emacs.)