Now splitting high-high generics in two subgroups: one group for
simple selectors, another group for complex selectors. Turns out
the great majority of high-high generics are simple selectors, and
simple selectors can be applied incrementally with DOM changes, as
opposed to complex selectors. This brings in a significant perf.
improvement in the processing of high-high generics (previously,
all high-high generic selectors were processed as one big complex
selector).
Aside extending cosmetic filtering abilities, I expect this will
also take care of some long standing issues (I will have to find them
and mark them as "resolved" by this commit, as time allow).
