Add support for other ways of triggering intermediate result outputs

Fio has support for using the USR1 signal to dump the current
results while continuing to run. Add a --status-interval parameter
to allow this to be configured to automatically happen every X
seconds.

There's also support for signaling fio through the file system. To
do that, simply touch /tmp/fio-dump-status. When fio sees this file,
it will unlink and dump the current results.

A small tweak is needed for the file approach to work in Windows.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/HOWTO b/HOWTO
index c7d0c9e..6445348 100644
--- a/HOWTO
+++ b/HOWTO
@@ -1600,6 +1600,9 @@
 
 It is also possible to get fio to dump the current output while it is
 running, without terminating the job. To do that, send fio the USR1 signal.
+You can also get regularly timed dumps by using the --status-interval
+parameter, or by creating a file in /tmp named fio-dump-status. If fio
+sees this file, it will unlink it and dump the current output status.
 
 
 7.0 Terse output
@@ -1721,7 +1724,7 @@
 
 
 9.0 CPU idleness profiling
-
+--------------------------
 In some cases, we want to understand CPU overhead in a test. For example,
 we test patches for the specific goodness of whether they reduce CPU usage.
 fio implements a balloon approach to create a thread per CPU that runs at