JAVA-1295: Using difference between the current and previous exception in ServerMonitor to determine whether to log a state change.
Fixed BSONTest.testUTF8 to ignore surrogate characters, which are not valid UTF-8 characters, so that the test passes on Java 8.
Fixed BSONTest.testUTF8 so that it compiles with Java 6.
Preparing for 2.12.3
Preparing for 2.12.4-SNAPSHOT