[MERGE] Only loop graph.iter_ancestry once when running "bzr log FILE"

[Gary van der Merwe]

Currently, when running "bzr log FILE", graph.iter_ancestry is been
looped through twice, once in get_view_revisions and once in
_filter_revisions_touching_file_id.

This patch changes it so that it is only looped through once in
get_view_revisions and passed to the functions that need it.

I thought this was going to increase the speed of "bzr log FILE" alot,
but it only made it a bit faster. I did not realize that the loading
of the graph is cached.

lifeless said I should still submit.

Quote from Irc:
<lifeless>	 the index layer does have a cache of its own, and the
majority of the cost of traversing is disk io and parsing, yes.
<lifeless>	 but with a big enough data set, the cache can be
exhausted, which would lead to duplicate IO
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