(PUP-398) Munge package source on Windows

Adding munge and slashreplace method to windows package provider
to ensure successful installation of packages.  Validation in the
type validate() not possible because we haven't chosen a provider
at that point.  Outputs debug as a means of notifying the user that
the source has been changed.
Merge pull request #2880 from fiddyspence/feature/2945/warning_on_windows_package_source

(PUP-398) Windows package provider source munging and test