In case we have a git clone from Linux that is accessed via cygwin git
the files executable status will be derived from the file content (shebang)
and won't match the git repo, leading to a initially dirty tree.
This can be worked around by setting "core.filemode=false", but let's try
to match the cygwin permissions with the in-repo permissions so this isn't
needed.
In WSL, we do not have `/usr/bin/winpty`. Let's verify that it is
available before using it, falling back to the `winpty`-less invocation.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
