help: collation support on Windows

According to the online documentation, the APIs are there:
http://msdn.microsoft.com/en-ca/library/a7cwbx4t.aspx

Now we'd need someone brave try to make it work.  The starting point
would be to define HAVE_LOCALE_T and then make it build.  Microsoft has
all the relevant functions and types with an underscore in front
(_strcoll_l, etc.), so some extra #defining will probably be necessary.

Also, initdb will need to be patched to get a list of OS locales to
populate the pg_collation catalog with.

Finally, a regression test customized for Windows, but I can help with
that later.