Replaced open_direct_file with open_file, which takes a flag about whether to use direct I/O.
Moved file_directness_t parameter up to filepath_file_opener_t constructor, with default value.
Made the io_backender_t hold the directness parameter.
Removed RSI comment about the no-longer-present directness argument to the filepath_file_opener_t constructor.
Added configurable --no-direct-io flag.
Made use of std::bind in place of boost::bind in command_line.cc.
Removed default value of file_directness_t param in io_backender_t constructor, made unit tests use buffered mode.
Renamed file_directness_t to a more serious, super-sounding professional name.
Merge branch 'next' into sam_1051
Renamed other uses of directness name to direct_io_mode.
Merge branch 'next' into sam_1051
Merge branch 'sam_1051' of github.com:rethinkdb/rethinkdb into sam_1051
Merge branch 'sam_1051' into next