LP#1709710: Make chunk sizing smart about XML quoting

LP#1709710: Make chunk sizing smart about XML quoting

XML inside JSON as a quoted string that's itself inside XML causes quite the
pile up of nested excaping of certain characters in OpenSRF PARTIAL_RESPONSE
messages.  Here we check for the worst offenders (<, >, &, and ") and account
for the cost of escaping them in chunked response stanzas.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>