send_message only drops the bytes in a buffer and a sync is needed to
avoid intermittent test issues. Change the name of the method to make
this more apparent during review.
-BEGIN VERIFY SCRIPT-
sed -i 's/send_message(/send_without_ping(/g' $( git grep -l 'send_message(' )
-END VERIFY SCRIPT-
Previously, `wait_for_getheaders` would check whether a node had received **any**
getheaders message. This implied that, if a test needed to check for a specific block
hash within a headers message, it had to make sure that it was checking the desired message.
This normally involved having to manually clear `last_message`. This method, apart from being
too verbose, was error prone, given an undesired `getheaders` would make tests pass.
This adds the ability to check for a specific block_hash within the last `getheaders` message.