* src/builtin.c (numeric_arg): Treat empty string as 0, with a

* src/builtin.c (numeric_arg): Treat empty string as 0, with a
warning.  Detect quoted leading space and overflow as warnings.
(m4_eval): Treat empty radix as 10, and allow output in radix 1.
Treat width as minimum number of digits, as required by POSIX.
(m4_ifdef, m4_divert, m4_m4exit, m4_translit): Ignore extra
arguments.
(m4_substr): Likewise.  Silently treat empty start as 0.
(m4_undivert): Treat ` 1a' as file, not diversion 1.
* src/eval.c (eval_lex): Parse radix 1 numbers.
* doc/m4.texinfo (Invoking m4): Fix wording; there is more than
one type of warning.
(Manual): Document behavior of numeric parsing of empty string.
(Divert, Incr): Document error handling.
(Eval): Document radices better.
(Incompatibilities): Document translit incompatibility.
* NEWS: Document these changes.