Fix read workload regression.
Removed file_account_t argument from index_write.
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
Make buffered I/O the default. --no-direct-io is now deprecated, --direct-io introduced instead.
merge of #2343 importing Python driver can cause namespace collisions
fix for a missing ast.

over-the-shoulder by @VeXocide
fix for #3409 `polyglot/transform/map.py` failing because of error text change

over-the-shoulder by @VeXocide
Kqueue event queue backend for OS X
Renamed a variable and fixed a typo.
fixes #3253 Installer artwork broken on Yosemite
Handle EINTR in kevent() call. Also added a newline to kqueue.cc to satisfy lint.