During fatal error, destroy all the data

I'll not worry about the data created by via strdup of yytext.
This data probably will leak just in case of unexpected end of
file. Also I fix the missing free over the identifier test.
Returning the yytext in lexema to bison/yacc
turning the variable test better

I'm changing the test of the not named variable to not copy the
yytext to the output. Probably the grammar will need do some sort
of appending or other stuff, but I can't reference in code a
variable started with '_'.