glacier:/opt/rainier/pkgsrc/wip/btpin-qt$ pkglint
FATAL: Assertion failed: Unknown line format: ./../../x11/qt3-libs/buildlink3.mk:36: .include "../../x11/libXcursor/buildlink3.mk" .
  line 7772 called main::main
  line 7766 called main::checkitem
  line 7735 called main::checkdir_package
  line 7618 called main::load_package_Makefile
  line 3459 called main::readmakefile
  line 3429 called main::readmakefile
  line 3364 called main::parselines_mk
  line 3346 called main::parseline_mk
  line 3338 called PkgLint::Util::assert
-libs/buildlink3.mk

I accidently had an extra space at the end of an .include line in the 
buildlink3.mk after the trailing quote.

When I removed that space, pkglint appeared to run fine.