only use colorsvn if it is found

jsvn

@@ -197,7 +197,7 @@ def main(argv):
             sys.stdout.write(getSVNRoot(realsvn) + '\n')
             return 0
 
-        if argv[0] in ('st', 'status', 'log'):
+        if argv[0] in ('st', 'status', 'log') and colorsvn != '':
             realsvn = colorsvn
 
     Popen([realsvn] + argv).wait()