Include string.h, for strlen.

Include string.h, for strlen.
(yyreportParseError): Use size_t for yysize.
(yy_yypstack): No longer nested inside yypstates, as nested
functions are not portable.  Do not assume size_t is the
same width as int.
(yypstates): Do not assume that ptrdiff_t is the same width
as int, and similarly for yyposn and YYINDEX.