For the boolean operators, the subset optimization works by calculating
the cheaper argument first, and passing the subset to the second
argument to restrict the revision domain. This works well for filtering
predicates.
But parents() don't work like a filter: it may return revisions outside the
specified set. So, combining it with boolean operators may easily yield
incorrect results. For instance, for the following revision graph:
0 -- 1
the expression '0 and parents(1)' should evaluate as follows:
0 and parents(1) ->
0 and 0 ->
0
But since [0] is passed to parents() as a subset, we get instead:
0 and parents(1 and 0) ->
0 and parents([]) ->
0 and [] ->
[]
This also affects children(), p1() and p2(), for the same reasons.
Predicates that call these (like heads()) are also affected.
We work around this issue by ignoring the subset when propagating
the call inside those predicates.
This adds support for r'...' and r"..." as string literals. Strings
with the "r" prefix will not have their escape characters interpreted.
This is especially useful for grep(), where, with regular string
literals, \number is interpreted as an octal escape code, and \b is
interpreted as the backspace character (\x08).
