#9824: encode , and ; in cookie values so that browsers don't split on them
There is a small chance of backward incompatibility here, but only for
non-SimpleCookie applications reading SimpleCookie generated cookies. Even
then, any such ap is likely to be handling escaped values already, and it would
take a fairly perverse implementation of unescaping to fail to unescape these
newly escaped chars, so the risk seems minimal.
........