stablesort: record, cache and reuse jump
Iterating below a merge means two things:
1) iterate over the part exclusive to the higher parents,
2) iterate from the lower parents.
While iterating on the exclusive part, there will be case were we just go the
next natural parent, and case were we'll have to "jump" to another revision. If
we record all point this "jump" happens and their target, we can easily
reproduce the iteration in the future. With that information we can iterate over
the exclusive part of the merge without having to compute it entirely.
In addition we store the reason of the jump. This will help the stable range
processing later.
[flake8]
ignore =
#closing bracket does not match indentation of opening bracket's line
E123,
# closing bracket does not match visual indentation
E124,
# visually indented line with same indent as next logical line
E129,
# at least two spaces before inline comment
E261,
# too many leading '#' for block comment
E266,
# expected 2 blank lines, found 0
E302,
# expected 2 blank lines after end of function or class
E305,
# module level import not at top of file
E402,
# line too long (82 > 79 characters)
E501,
# do not assign a lambda expression, use a def
E731,
# class names should use CapWords convention
N801,
# line break occurred before a binary operator
W503
builtins=xrange, execfile