qapi: Rename 'dirty-bitmap' mode to 'incremental'

If we wish to make differential backups a feature that's easy to access,
it might be pertinent to rename the "dirty-bitmap" mode to "incremental"
to make it clear what /type/ of backup the dirty-bitmap is helping us
perform.

This is an API breaking change, but 2.4 has not yet gone live,
so we have this flexibility.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1433463642-21840-2-git-send-email-jsnow@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/qmp-commands.hx b/qmp-commands.hx
index a05d25f..87fa172 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1137,10 +1137,10 @@
             (json-string, optional)
 - "sync": what parts of the disk image should be copied to the destination;
   possibilities include "full" for all the disk, "top" for only the sectors
-  allocated in the topmost image, "dirty-bitmap" for only the dirty sectors in
+  allocated in the topmost image, "incremental" for only the dirty sectors in
   the bitmap, or "none" to only replicate new I/O (MirrorSyncMode).
-- "bitmap": dirty bitmap name for sync==dirty-bitmap. Must be present if sync
-            is "dirty-bitmap", must NOT be present otherwise.
+- "bitmap": dirty bitmap name for sync==incremental. Must be present if sync
+            is "incremental", must NOT be present otherwise.
 - "mode": whether and how QEMU should create a new image
           (NewImageMode, optional, default 'absolute-paths')
 - "speed": the maximum speed, in bytes per second (json-int, optional)