[PATCH] Update ASTGrammar for lang/PIR

[Klaas-Jan Stol]

hi,

attached an update for ASTGrammar.tg for languages/PIR

In order to print the past tree to screen, set 'target' to 'past' in
pirc.pir. Currently, it is set to 'parse' in order to pass the tests.

regards,
klaas-jan