[MERGE] improvements to parse_line_delta_iter

[John Arbash Meinel]

The current Knit.parse_line_delta is written such that it takes a list,
and slowly removes lines from the beginning of this list. This is wrong
because:

1) It means the list you pass in is destroyed, so if you want to keep
it, you have to do a copy.

2) It is slow to pop things off the beginning of a list. So it is better
to pull them off the end. Or better yet, don't pop anything off, and
just iterate using a counter.

I did the latter in this patch. It shaves another 350ms or so off of the
time to iterate through all of my inventory.knit during
fileids_altered_by....

Also, I caught a small bug where parse_line_delta_iter for a different
factory was bogus. It was using function[] rather than function(), but I
changed it around anyway.

John
=:->
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