Keep ICAP connection persistent after an OPTIONS response if possible.

Keep ICAP connection persistent after an OPTIONS response if possible.

Old OptXact code used Xaction::doneReading() which was only true at EOF.
Thus, closeConnection() was thinking we are still reading (i.e., not
doneWithIo) at the end of the transaction and force-closed the connection.

New OptXact implements its own doneReading() which returns true at EOF and
when we read the entire response. Since we cannot parse OPTIONS body and
do not know where it ends, OPTIONS responses with bodies still result in
connection closure. We should not be getting any, but there are broken ICAP
servers that do send them. Hopefully, they all use Encapsulated: opt-body.