Bug with new iteration code in parse

parse is currently broken when trying do use an AbstractString whose eltype is not Char, but some other type of AbstractChar.
The issue is that the code has a type assertion ::Tuple{Char,Int} on the calls to iterate, instead of ::Tuple{eltype(s),Int}.
This breaks the Strs.jl package.

I have placed a fix in https://github.com/ScottPJones/julia/tree/spj/fixparse, if somebody can pull that in to julia as a PR.