DATAMONGO-682 - Performance improvement for mapping hotspots.

This commit includes the MongoDB specific parts for the mapping subsystem performance improvements. Reworked PerformanceTest to output more reasonable numbers.

Heavily inspired by Patryk Wasik's contribution at https://github.com/SpringSource/spring-data-mongodb/pull/37.

GitHub PR: #37
Conflicts:
	spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/mapping/MappingTests.java