All SSL tests can now be run under various configurations.
MOTOR-45 Add socketKeepAlive option.

You can now do MotorClient(socketKeepAlive=True), or
MotorReplicaSetClient(socketKeepAlive=True).
Longer timeout for test_high_concurrency.
Unused import.
Update some Synchro properties.

Fixing failures running PyMongo 2.8's tests with synchrotest.
synchrotest skips TestExhaustCursor.

These tests need to be reimplemented for Motor.
Add MotorGridFS.find_one().

It takes any query, or no query, and returns one MotorGridOut.
Synchro need not emulate MongoClient's ConfigurationError exception.
Update a comment in synchrotest.
PyMongo's test_paired.py is long gone.
Update list of skipped PyMongo tests in synchro.
Mock some new PyMongo private properties for Synchro.