(emdnorm, eifrac, euifrac, mtherr): Replace
unconditional `pedwarn' by `warning' conditional on `extra_warnings'.
(toe24, todec): Use ERANGE to flag overflow on (non-IEEE)
machines that do not have infinity.
(etoasc): Check explicitly for overflow of leading decimal digit.
(asctoeg): Test for, and immediately reject, out-of-bounds
decimal exponent inputs.
(at top level): Include errno.h; reference errno, warning, extra_warnings.

From-SVN: r4300