- The "id_re_with_port" regex was too lax, and let through many illegal strings just because they contained colons. Fix it to require that both the ID and port component be independently safe.
- Even when the code detected that a string needed quoting, ", \n, and \r were left alone inside the double quotes, which is illegal. Replace them with appropriately escaped versions.
We also add a test that pydot is correctly able to quote Python's "string.printable" string, which exercises both of the above cases.
git-svn-id: http://pydot.googlecode.com/svn/trunk@18 06aa9b79-7134-0410-ae7e-c1cd3e483e87
