bsongen: handle nesting with unique var names
bsongen: prefix local vars with _
bsongen: more tweaks
bsongen: better bson.Null handling
bson: encode maps & slices as empty if nil.

I was encoding them as bson.Null, but existing
clients expect empty objects instead. Legacy wins.
bson: change custom encoders to not use Null for slices and maps
bson: RecordLen -> Close
bson: improved nil value handling for custom marshalers
Implemented re-resolve on error for topology and added tests.
removed superfluous line from test.
Cleanup for readability and corresponding changes to tests.
Minor cleanup for readability.
First pass at vttablet health check.

Moving a lot of stuff around too.
queryservice: /debug/schema and /schemaz
Implementing rebuild for tablet health.
Merge branch 'vtocc'
Adding test for health check.

And fixing associated bugs.
Comment fix.
Health modules: initial version of the framework.
Health checks for MySQL.