[phobos] Commit 1717 broke Phobos unittests

[Don Clugston]

conv.d, in the parse function for floating point numbers:
Target parse(Target, Source)(ref Source p) if (isInputRange!Source &&
/*!isSomeString!Source && */isFloatingPoint!Target)

The offending line is line 1360:
enforce(anydigits);

This is wrong; it should be throwing ConvError. This makes the
unittests in line 2257, 2312, 2380 fail.

In fact, most of the other uses of enforce() in this function should
probably be throwing a ConvError.