MinGit: use the Git wrapper as ash.exe, if possible

Some programs, such as OpenSSH, require the environment variable `SHELL`
to contain an absolute path to an executable. No extra arguments
allowed.

However, BusyBox' `ash` would need to be called like this:

	<mingit>\mingw64\bin\busybox.exe sh [...]

If the `sh` is omitted, only mayhem will ensue.

To allow for setting `SHELL` in such a manner, we taught the good ole'
Git wrapper to stand in. That is, if the Git wrapper detects that it is
run with the base name `ash.exe` (or `sh.exe`), it will try to spawn
BusyBox' `ash` with the same argument, wait for the command to conclude,
and then exit with the same exit code.

Let's use this version of the Git wrapper, if we have it.

This requires git-for-windows/MINGW-packages#52
to work, and allows e.g. using a `ProxyCommand` with OpenSSH, after
setting `SHELL` to point to the `ash.exe` file.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

mingit/release.sh

@@ -156,6 +156,18 @@ then
 	esac
 fi
 
+# Use git-wrapper.exe as ash.exe if supported
+if test -f "$SCRIPT_PATH/root/$BIN_DIR"/busybox.exe
+then
+	# verify that the Git wrapper works
+	cp "/mingw$BITNESS/share/git/git-wrapper.exe" "$SCRIPT_PATH/root/$BIN_DIR"/ash.exe
+	uname="$($SCRIPT_PATH/root/$BIN_DIR/ash.exe -c uname 2>&1)"
+	case "$?,$uname" in
+	0,*BusyBox*) ;; # okay, let's use the Git wrapper
+	*) rm "$SCRIPT_PATH/root/$BIN_DIR"/ash.exe;;
+	esac
+fi
+
 test ! -f "$TARGET" || rm "$TARGET" || die "Could not remove $TARGET"
 
 echo "Creating .zip archive" &&