linspace: raise errors for cases that cannot be constructed.

E.g. linspace(realmin(), realmax(), maxintfloat())

base/range.jl

@@ -208,12 +208,16 @@ function linspace{T<:FloatingPoint}(start::T, stop::T, len::T)
  end
  end
  end
- if isinf(n*start) || isinf(n*stop)
- n, p = frexp(n)
+ a, c, s = start, stop, n
+ if isinf(a*n) || isinf(c*n)
+ s, p = frexp(s)
  p = one(p) << p
- start /= p; stop /= p
+ a /= p; c /= p
  end
- return LinSpace(start, stop, len, n)
+ if a*n/s == start && c*n/s == stop
+ return LinSpace(a, c, len, s)
+ end
+ error("linspace($start, $stop, $len): cannot be constructed")
 end
 function linspace{T<:FloatingPoint}(start::T, stop::T, len::Real)
  T_len = convert(T, len)