More work on MSI building

Makefile is now capable of farming the building of the MSI out to the
AWS winbuild instance, which in turn is controllable thru the new
winbuild script in the windows sub-directory. Things still to fix:

 * Get the license right in the constructed MSI
 * Bundle the AWS instance up as an AMI to ensure state is not preserved
   between packaging runs
 * Try out pyinstaller as an alternative to py2exe