[boost] [algorithm] Two comments

Hi, I started using the filter/split-iterators from the string-algorithm. today, and liked them a lot. However, I think some improvements would make them even better: 1. Provide const overloads for make_foo_iterator funcs. Currently, I can't use those functions to search f.ex. a const std::string. Works fine when using the constructor directly though. 2. Make the filter_type public or templated (with boost::function as default). Simply because I'd like to avoid dynamic memory allocation when in functions creating those iterators. It feels a bit unnecessary and I can't create something of filter_iterator_base::finder_type, since it's protected. Does it sound reasonable? Cheers, /Marcus