refs #1111, change show collections to not display size if TOKUMX_SHOW_NO_SIZES environment variable is set where mongod is running
added CONTRIBUTING file
prevented draining shards from being picked #1069

This avoids a confusing situation with a draining shard getting overloaded
by data in a new database which picks it as primary, or by sequential
insert optimizations splitting a chunk unevenly.

fixes #1069