localrepo: move filtername to __init__...
localrepo: move filtername to __init__
This is obviously an instance attribute, not a type attribute. The
modern Python style is to use __init__ for defining these.
This exposes statichttprepo as inheriting from localrepository
without calling its __init__. As a result, its __init__ defines
a lot of variables that methods on localrepository's methods need.
But factoring the common bits into a separate class is for another
day.
