INT-3283: Prevent `AbstractSelectableChannel` NPE

JIRA: https://jira.springsource.org/browse/INT-3283

INT-3236: Remove deprecated `AbstractConnectionFactory.close`

JIRA: https://jira.springsource.org/browse/INT-3236

INT-3283: Remove `selectorLock`

As far as the issue in JVM's `AbstractSelectableChannel` was fixed in Java 7 and 8,
just catch entire `Exception` on `stop()`.