Fix `string-to-number' to deal consistently with integers and floats.

Fix `string-to-number' to deal consistently with integers and floats.
* lread.c (isfloat_string): New argument ignore_trailing to accept all
  trailing characters, not just whitespace.
  (read1): Pass new arg 0 to keep old behavior.
* data.c (Fstring_to_number): Pass 1 to isfloat_string to ignore
  trailing chars, as it is already done for integers.  Doc fixes.
* lisp.h (isfloat_string): Add new arg to declaration of isfloat_string.