User visible:
* Also accept the git install path (and not the mingw64 subdir) as a user
supplied install location. Make it the new default and warn the user if
a mingw64 dir is supplied (=this dir is not checked, so it might be
anywhere...)
* Find git.exe in path and use that as an install location
* Add error|status messages and output less noise (robocopy)
* do some check if column.exe is not found...
* adjust the installation text for windows...
not user visible:
* more.exe does not work when used in a cmd which has a unicode codepage
-> save the current codepage and set a sane default during the install
* do some "magic" with quotes around path variables -> makes it work with
pathes with spaces in it (both final git dir and the git-extra checkout)
* Do not leak variables to the sourounding interpreter
