First draft
WIP
Type inference works correctly
Remove left over caddddr
Fix Splatting
Ugly version of error handling

This will have to be changed once we switch the way we do func_for_method,
but I will await @JeffBezanson's judgement on how to do that best, so I'll
use this to go head first.
For caching staged methods, don't restrict the number of varargs to match

Also adds `stagedfunction` as a keyword to Kate's julia.xml file
Simplify conditional in jl_method_table_assoc_exact
stagedfunctions: specialize for all input types
Expand stagedfunction tests
Rename t1 to avoid collision with bitarray tests
Merge pull request #7474 from JuliaLang/kf/staged

WIP: Staged functions