MCO-325 - update win32 instructions to point at 1.9.3

MCollective runs acceptably well on 1.9.3 on windows.  It's what
we ship in PE and also what the unofficial .msi uses.
Merge pull request #194 from richardc/MCO-325_windows_readme

MCO-325 - update win32 instructions to point at 1.9.3