added "root" subcommand

jsvn

@@ -185,6 +185,10 @@ def main(argv):
             Popen([colordiff], stdin=diff_out).wait()
             return 0
 
+        if argv[0] == "root":
+            sys.stdout.write(getSVNRoot(realsvn) + '\n')
+            return 0
+
     if colorsvn != '':
         realsvn = colorsvn