cluster: add debug message when unexpectingly connecting to sharded cluster
client: close urandom fd after seeding rand.
removal of aggregate_legacy + new cursor interface

o made aggregate work for wire_version 0 or 2
o Added in mongoc_cursor_interface_t and a synthetic cursor stub to
  handle the aggregate modes.
cursor: cleanup some gcc warnings.
adding OP_QUERY rpc exhaust support

Provide suport for exhaust queries

Found a couple of bugs in:
* buffers didn't handle already buffered data well (negative unsigned
  ints
* gridfs files were still on possibly negative min_bytes for readv