Fix for double backslashes in paths to programs in shell/open etc.
registry entries for all non-native file types such as .doc that are
mapped by installer to use scalc.exe/swriter.exe etc.

Change-Id: Ice8033d4fee079c0fb6d8f84e00ebd784e85d135
Reviewed-on: https://gerrit.libreoffice.org/25849Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: jan iversen <jani@documentfoundation.org>