Refactor IntSets to use BitVectors

* Use BitVectors instead of a mismash of bitvector.c and ad-hoc Julia code.
* Invert the complement IntSet semantics.  Instead of filling ones outside the range of the IntSet, simply reverse what a set bit means.
* For mathematical functions (intersect, union, etc.), use BitVector functions to work 64 bits at a time instead of working bit-by-bit.
* Increase test-coverage to 100%

base/coreimg.jl

@@ -57,6 +57,7 @@ include("functors.jl")
 include("reduce.jl")
 
 ## core structures
+include("bitarray.jl")
 include("intset.jl")
 include("dict.jl")
 include("iterator.jl")

base/hashing.jl

@@ -62,7 +62,6 @@ else
     hash(x::Expr, h::UInt) = hash(x.args, hash(x.head, h + 0x96d26dc6))
 end
 
-
 # hashing ranges by component at worst leads to collisions for very similar ranges
 const hashr_seed = UInt === UInt64 ? 0x80707b6821b70087 : 0x21b70087
 function hash(r::Range, h::UInt)