[MERGE/RFC] Use _read_records_iter_unchecked in _get_remaining_record_stream.

[Robert Collins]

Robert Collins has voted tweak.
Status is now: Conditionally approved
Comment:
If you put a check similar to what iter_records_raw does when inserting 
a knit format record in insert_record_stream, then its shifting A->B, 
and less server load in branching full branches (which is arguably more 
common than uploads of entire histories).

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090306005040.GA857%40steerpike.home.puzzling.org%3E
Project: Bazaar