SERVER-13635: add a method to RecordStore and Collection to lookup by DiskLoc that might not exist
SERVER-13635: fix cloner using system.namespaces
SERVER-14425 Fix a bug in the Lock Manager for the conversion path

The mode counts were not being maintained correctly and this was
introduced by commit 22b368a74b36896de6b164c55cd4b3b9ca562bb2.

This change also adds additional assertions to help catch such issues in
the future.
Merge remote-tracking branch 'upstream/master'