[Gm2] RealConv.mod first cut

[Gaius Mulley]

Hi,

here are the latest cvs additions and in particular
gm2/gm2-libs-iso/RealConv.mod has been implemented.  Also three new
runtime regression tests accompany the library.

In time I plan to replace the internals of
gm2-libs/StringConvert.mod:LongrealToString by a call to dtoa.c which
will perform a much more accurate conversion.

regards,
Gaius

  * gm2/gm2/Make-lang.in:  RealConv.mod new file.
  * gm2/gm2/gm2builtins.c:  added __builtin_log10f,
    __builtin_log10 and __builtin_log10l.
  * gm2-libs/Builtins.def:  added definitions for
    log10f, log10, log10l, exp10f, exp10, exp10l.
  * gm2-libs/Builtins.mod:  new functions
    log10f, log10, log10l, exp10f, exp10, exp10l.
  * gm2/gm2-compiler/M2Quads.mod:  migrated more error
    messages to use M2MetaError and also made
    BuildTruncFunction recover if operands are the wrong type.
  * gm2/gm2-libs/StringConvert.def:  ToSigFig new function.
  * gm2/gm2-libs/StringConvert.mod:  re-factored to use IsDigit.
    Implemented ToSigFig.  StringToLongreal improved to
    minimise floating point operators.  LongrealToString
    now allows TotalWidth of zero in which case it keeps
    converting until the precision is exhausted.
  * gm2/gm2-libs/cbuiltin.def:  new definitions log10f,
    log10, log10l, exp10, exp10l, exp10f.
  * gm2/gm2-libs/libm.def:  new definitions exp10, exp10l,
    exp10f.