Log Message:
Bump version to	pkg_chk-1.91:
* Look for $MAKECONF in @MAKECONF@, @PREFIX@/etc/mk.conf,
  and /etc/mk.conf, in that order.
* Look for $PKGSRCDIR in the Makefile referred to by $MAKECONF,
  ".", "..", "../..", and "/usr/pkgsrc", \ 
in that order.
* Convert the Makefil to use the SUBST framework.

Proposed in tech-pkg; OK (in principle) David Brownlee