Better fix of Rational-to-BigFloat ambiguity warning

(reverts a85476b)

Author: carlobaldassi

base/mpfr.jl

@@ -82,7 +82,7 @@ BigFloat(x::Union(Float16,Float32)) = BigFloat(float64(x))
 BigFloat(x::Rational) = BigFloat(num(x)) / BigFloat(den(x))
 
 convert(::Type{Rational}, x::BigFloat) = convert(Rational{BigInt}, x)
-convert(::Type{BigFloat}, x::Rational) = BigFloat(x) # to resolve ambiguity
+convert{S}(::Type{BigFloat}, x::Rational{S}) = BigFloat(x) # to resolve ambiguity
 convert(::Type{BigFloat}, x::Real) = BigFloat(x)
 convert(::Type{FloatingPoint}, x::BigInt) = BigFloat(x)
 

base/rational.jl

@@ -45,7 +45,7 @@ convert(::Type{Bool}, x::Rational) = (x!=0) # to resolve ambiguity
 convert{T<:Integer}(::Type{T}, x::Rational) = (isinteger(x) ? convert(T, x.num) : throw(InexactError()))
 
 convert(::Type{FloatingPoint}, x::Rational) = float(x.num)/float(x.den)
-function convert{T<:FloatingPoint,S<:Integer}(::Type{T}, x::Rational{S})
+function convert{T<:FloatingPoint,S}(::Type{T}, x::Rational{S})
     P = promote_type(T,S)
     convert(P,x.num)/convert(P,x.den)
 end