[win32] GRE in mozilla trunk builds

[Sean Su]

Dougt, Seawood, and I have just checked in code that will enable the 
mozilla trunk builds to install GRE in a shared location for win32 
platforms only.  The global, shared location is:
 [Common Files]\mozilla.org\GRE\[gre version]

Even though GRE will be installed in a global area, it will not conflict 
with builds from different days.  Each daily mozilla build will install 
its GRE into a unique directory name.  For example, for milestone 1.4a 
and a build ID of 2003031217, the unique GRE dir name will be:
 [Common Files]\mozilla.org\GRE\1.4a_2003031217

This will allow the mozilla community to install nightly builds in 
different differectories without having the GRE clash from nightly build 
to nightly build.

This change will show up starting with tomorrow's mozilla build.