SERVER-7588 Improve logic for seconds and milliseconds in ISODate constructor

Do not use floating point for seconds, only for milliseconds. Adjust other
date components when milliseconds round up to 1000.

Code backported from Tad Marshall's master branch commit:
https://github.com/mongodb/mongo/commit/7cf042ff3e0c97a7fe701cd85f5cdd4c1519179b
SERVER-10039 sorting ignored in returned query obj for differ
SERVER-10039 buildbot test ChunkManagerLoadBasicTest need index to support sorting chunks in test
SERVER-10478 fix batch limit check for _cloneLocs in migration

Conflicts:
	src/mongo/s/d_migrate.cpp
SERVER-10498 print conn pool stats and ensure migration succeeds before testing error
version bump to mongodb 2.2.6
added NEWS about 2.2.6
Merge branch 'merge-2.2.6'

Conflicts:
	distsrc/NEWS
	src/mongo/util/version.cpp

fixes #436