Phobos math expert wanted: Please help porting std.conv.parse to 64bit reals

[Johannes Pfau]

std.conv.parse!(real) and therefore also parse!double, parse!float were
written assuming real is always a 80 bit type. But on most non x86
systems the largest floating point type is actually double and
therefore real is basically an alias for double. std.conv makes some
convenient assumptions for 80bit reals (like mantissa size is ==
long.sizeof). I guess this is a simple fix for math/floating point
experts but I'd need quite some time to fix it. So it'd be great if
someone could help and port std.conv.parse to systems with 64 bit reals
(real.mant_dig == 113) :-)

https://github.com/D-Programming-Language/phobos/blob/master/std/conv.d#L2367