git-gui: add mingw specific startup wrapper

The wrapper adds the directory it is installed in to PATH.
This is required for the git commands implemented in shell.
git-gui fails to launch them if PATH is not modified.

The wrapper script also accepts an optional command line
switch '--working-dir <dir>' and changes to <dir> before
launching the actual git-gui. This is required to implement
the "Git Gui Here" Explorer shell extension.

As a last step the original git-gui script is launched,
which is expected to be located in the same directory
under the name git-gui.tcl.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

windows/git-gui.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+# Tcl ignores the next line -*- tcl -*- \
+exec wish "$0" -- "$@"
+
+if { $argc >=2 && [lindex $argv 0] == "--working-dir" } {
+	cd [lindex $argv 1]
+	set argv [lrange $argv 2 end]
+	incr argc -2
+}
+
+set gitguidir [file dirname [info script]]
+regsub -all ";" $gitguidir "\\;" gitguidir
+set env(PATH) "$gitguidir;$env(PATH)"
+unset gitguidir
+
+source [file join [file dirname [info script]] git-gui.tcl]