git-gui: fix PATH environment for mingw development environment

When creating a desktop shortcut from the gui the shortcut directly
starts wish with the git-gui script. In the msysgit development
environment some dll's reside in the mingw/bin directory which causes
that git can not start because libiconv2.dll is not found.

When using such a link the error is even more cryptic stating:
"child killed: unknown signal"

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

windows/git-gui.sh

@@ -13,10 +13,11 @@ if { $argc >=2 && [lindex $argv 0] == "--working-dir" } {
 	incr argc -2
 }
 
-set bindir [file dirname \
+set basedir [file dirname \
             [file dirname \
              [file dirname [info script]]]]
-set bindir [file join $bindir bin]
+set bindir [file join $basedir bin]
+set bindir "$bindir;[file join $basedir mingw bin]"
 regsub -all ";" $bindir "\\;" bindir
 set env(PATH) "$bindir;$env(PATH)"
 unset bindir