test.pn should not depend on libp2
greg-0.4.5: add yyerror, add filename, input, lineno

add YY_ERROR(G, message)
revamp YY_INPUT (G as first arg)
use G->input as new default input stream for YY_INPUT and YY_ERROR
initialize input, filename, lineno in parse_new
add filename to potion_parse for diagnostics
yyqq: escape % to %%
remove undeclared and unneeded GREG* from yyprintcontext
define DEBUG_PARSE, DEBUG_VERBOSE for YY_DEBUG (tested ok)
use YY_ERROR in potion+p2