Add THIS_IS_MSYSGIT for Git's Makefile to pick up the correct configuration

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
mingw32-unzip: Add mingw version of unzip

The vailable msys version of unzip causes some tests from
t5003-archive-zip.sh from the git test suite to either hang indefinitly
or fail.

Signed-off-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
Add a package description file for mingw32-unzip

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>
installer: Use mingw32-unzip by default in order to fix t5003-archive-zip.sh

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>