Don't use --dirty in genversion.bat.

This script updates version.mk, which is under version control,
so the tree is always dirty. Until the script is updated to write
package_version instead, incorporating version.mk as a fallback
the way update_version does, it's better not to use --dirty.

win32/genversion.bat

@@ -2,7 +2,7 @@
 
 setlocal enableextensions enabledelayedexpansion
 
-for /f %%v in ('git --git-dir="%~dp0..\.git" describe --tags --match "v*" --always --dirty') do set version=%%v
+for /f %%v in ('git --git-dir="%~dp0..\.git" describe --tags --match "v*" --always') do set version=%%v
 
 if not "%version%"=="" goto :gotversion