Comparison with Rational

[jmkuhn]

julia> d64"0.1" == 1//10
false

This should be true. Fixing this (and issue #79) is important to get hash() working (issue #97).

[stevengj]

This is calling ==(x::AbstractFloat, q::Rational), which assumes binary floating-point.

A correct implementation is probably something like:

function ==(x:: DecimalFloatingPoint, q::Rational)
    if isfinite(x)
        ispow10(q.den) & (x*q.den == q.num)
    else
        x == q.num/q.den
    end
end

[jmkuhn]

Also need to implement Base.decompose()

julia> d64"0.3" < 1//3
ERROR: MethodError: no method matching decompose(::Dec64)
Closest candidates are:
  decompose(::BigFloat) at hashing2.jl:133
  decompose(::Float64) at hashing2.jl:122
  decompose(::Float32) at hashing2.jl:111
  ...
Stacktrace:
 [1] <(::Dec64, ::Rational{Int64}) at ./rational.jl:316
 [2] top-level scope at REPL[3]:1