fixed readfile() fd-leak.

fixed readfile() fd-leak.

guys, always remember that every function that *generates output* could cause a
bailout if ignore_user_abort is set to false (and the user _aborts_ the
connection). in this case a longjump will be performed and our function (in
this case readfile) will have no chance to clean-up. having said that it's a
good idea to register all opened files using REGISTER_RESOURCE - that way the
engine will make sure they get closed on request end.