Windows: Compute the fallback for exec_path from the program invocation.
Windows: Compute the fallback for exec_path from the program invocation.

Since on Windows the user is fairly free where to install programs, we
cannot rely on a hard-coded path. We use the program name to derive the
installation directory and use that as exec_path.

Signed-off-by: Johannes Sixt <5cc107486946fdcf16e86d7c808fa50f4312125f@telecom.at>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git