Rewrite posixaio back off comment to be closer to actual English

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/engines/posixaio.c b/engines/posixaio.c
index 867b5f7..a84eb77 100644
--- a/engines/posixaio.c
+++ b/engines/posixaio.c
@@ -186,7 +186,9 @@
 	if (ret) {
 		/*
 		 * At least OSX has a very low limit on the number of pending
-		 * IOs, so if it will return EAGAIN.
+		 * IOs, so if it returns EAGAIN, we are out of resources
+		 * to queue more. Just return FIO_Q_BUSY to naturally
+		 * drop off at this depth.
 		 */
 		if (errno == EAGAIN)
 			return FIO_Q_BUSY;