Debugging support: yyprintf DO action name, one-line @ "context"

add defined arg to findRule,makeRule to catch rule defined but not used,
add action name to yythunk for run-time debugging
yyprintcontext prints the context for G->text, yytext or G->buf+G->pos only until the next newline
add yyqq to print quotable strings
pass yyDo action names
fix yymatchChar '\\'
print yymatchClass [] strings
check for needed realloc of G->vals on yyPush
Makefile: fix test target, add bootstrapping rule,

usage: try make OFLAGS=-DYY_DEBUG
and then greg -v or even greg -vv