[MERGE] Add timing to debug information for -Dhpss

[Ian Clatworthy]

Ian Clatworthy has voted tweak.
Status is now: Conditionally approved
Comment:
This needs a NEWS entry and a section added to 
doc/developers/profiling.txt. (Stuff like this is always welcome but we 
need to ensure developers know about it.)

Also, is there a good reason why you don't look for hpss in debug flags 
(and mutter if found) before the previous return statement (line 377) in 
the read_body_bytes() method?

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C46AFABA7.4070504%40arbash-meinel.com%3E