Add doc count estimates to r.table.info().
Add integration test for doc_count_estimates in table.info().
Improve wording of comment
Show doc count statistics for system tables too.
Minor stylistic nitpicking.
Update interface.table_doc_count_estimates test.
Tweak factors in interface.table_doc_count_estimates
Merge branch 'tim/2980-distribution-2' into reql_admin