Explicitly detect invalid gle reuse when using 'releaseConnectionsAfterResponse' mode

If a application disobeys the always-gle-after-write requirements for the 'releaseConnnectionsAfterResponse' mode, we may not explicitly detect the failure but instead potentially return bad data from potentially another connection.

Potential fix - method in ClientConnections::areAllAvailable( const vector<string> gleHosts ) and logic block in ClientInfo::getLastError() which throws a "incorrect use of gle in 'release connections after response' mode" error.