Type instability in parametric functions not checked

[ArchRobison]

This may be a research project to fix.

checklooptypes seems to not find any issues with the following code that uses 0 where it should use zero(T).

julia> function tally{T}( a::Vector{T} )
           s = 0
           for x in a
               s += x
           end
           s
       end
tally (generic function with 1 method)

julia> checklooptypes(tally)
TypeCheck.LoopResults(:tally,TypeCheck.LoopResult[])

Of course the type instability shows up only for certain instances of T. Maybe the module checker could check all instantiations used in the module?