Fix read workload regression.
Removed file_account_t argument from index_write.
fix deadlock on errors in the backup scripts
Update mk/README.md
Use a common file account for block writes in the merger serializer to improve write I/O efficiency.
Merge branch 'next' into daniel_3377
Merge branch 'mlucy_3354' into next
Merge branch 'daniel_3377' into next
Disable OS' read-ahead when using buffered i/o on Linux.
Disable read-ahead on OS X as well.
Revert "Disable read-ahead on OS X as well."

This reverts commit 3cb0b7fa57cb7b24fd38c63c269a025d4719fd54.
Disable read-ahead on OS X as well.
Merge branch 'daniel_fadvise' into next
initial commit for #2343 importing Python driver can cause namespace collisions
adding import tests and making r/rethinkdb subclasses of object
Merge branch 'larkost/2343-python-import-star' of https://github.com/rethinkdb/rethinkdb into larkost/2343-python-import-star