[WIN32] fixed: git revision in build setup file name.

refactored the git version extraction code to be shared between the update_git_rev.bat and BuildSetup.bat scripts.
(cherry picked from commit f833d1e)

project/VS2010Express/update_git_rev.bat

@@ -6,34 +6,7 @@ IF EXIST %REV_FILE% (
   del %REV_FILE%
 )
 
-rem Use tgit.exe of TortoiseGit if available
-SET GITEXE="tgit.exe"
-%GITEXE% --version > NUL 2>&1
-if errorlevel 1 goto :notgit
-GOTO :extract
-
-:notgit
-
-rem Fallback on msysgit, which must have been added manually to the path.
-SET GITEXE="git.exe"
-%GITEXE% --help > NUL 2>&1
-if errorlevel 1 goto :nogit
-GOTO :extract
-
-:nogit
-
-rem Failure - no git tool to extract information.
-SET GIT_REV=Unknown
-GOTO :extracted
-
-:extract
-
-set oldCurrentDir=%CD%
-cd ..\..
-FOR /F "tokens=1 delims= " %%A IN ('%GITEXE% rev-parse --short HEAD') DO SET GIT_REV=%%A
-cd %oldCurrentDir%
-
-:extracted
+CALL ..\Win32BuildSetup\extract_git_rev.bat
 
 copy "%TEMPLATE%" "%REV_FILE%"