bug#16293: 24.3.50; doc of `string-to-number'

[Drew Adams]

Say what happens if STRING cannot successfully be parsed as a number:
the function raises an error.

The doc (e.g. manual) describes the parsing in a fair amount of detail,
and it describes how the result can end up a floating-point number if
the integer value would be too large.  But it says nothing about what
happens if no number can be identified for the string.



In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-12-27 on ODIEONE
Bzr revision: 115778 rgm@gnu.org-20131228000456-1797o8z6veuyozs0
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3' LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'