log: pack filematcher and hunksfilter into changesetdiffer object
This is just a way of getting rid of clumsy makefilematcher/makehunksfilter
arguments. There might be a better abstraction, but I don't think this is bad.
This makes filematcher and hunksfilter available by default, but that should
be fine.
log: drop dead code to concatenate --line-range patterns and pats
It's disabled since 2e45bbd3db7b, and the current implementation is unlikely
to be reused.