svn:ignore build directory; clean build by removing build dir

git-svn-id: svn+ssh://svn.psi-im.org/home/psi/svn/win-installer/trunk@39 2d3a5ac0-73f9-4639-b284-2310bd1da355

Makefile

@@ -15,6 +15,4 @@ build:
 	cd src; makensis psi.nsi
 
 clean:
-	rm -rf build/psi_app
-	rm -f build/*.nsh
-	rm -f build/*.exe
+	rm -rf build