The Linux ed command writes line numbers to stderr, redirect both
stdout and stderr to keep things quiet.
Add a new OS-layer function __wt_fsync_async to flush a file without
waiting for the results, call it from the Btree flush-leaves code so
pages start flushing while we're working the rest of the checkpoint.
Reference #1136.
FreeBSD doesn't have sync_file_range, add "unused" macros for the
__wt_fsync_async function's arguments.
Don't flush leaf pages asynchronously for now; reference #1152.
Clean up 3a8ed75, I was sloppy.
Merge branch 'develop' into async-doc
Review/edit the new asynchronous doc page, lots of random
cleanup/simplifications (at least, hopefully, they cleanup
and/or simplify).