Allow building Wattsi when there is no .git directory

This is helpful for Docker where we don't want to keep the .git directory around.

src/build.sh

@@ -19,7 +19,7 @@ PATHS="-Fu${SRC}html -Fi${SRC}html -Fi${SRC}html/entities.inc"
 DEFINES="-dUSEROPES -dLINES -dPARSEERROR"
 
 echo "Writing $VERSION_FILE"
-git rev-list --count HEAD > "$VERSION_FILE"
+(git rev-list --count HEAD || echo unknown) > "$VERSION_FILE"
 . ${SRC}lib/compile.sh
 echo "Removing $VERSION_FILE"
 rm "$VERSION_FILE"