adding compatibility to use rsync in kitchen-sync on mingw environment

[ashokf458]

Kitchen-sync rsync.rb is updated to add compatibility of working on mingw environment:

• allowing rsync to run as command from any location so long as it is available, and
• window type fullpath and their conversion to allow working with rsync.

[ashokf458]

using command availablitiy check using system command instead of mkmf libraries, was unnecessary