Adjusting pkg_chk to spend less time cleaning

[David Brownlee <abs%absd.org@localhost>]

By default pkg_chk calls

${MAKE} update CLEANDEPENDS=yes

which is great for leaving everything clean afterwards, but results in
a lot of time with every package cleaning all its depends... (it uses
this if the target package is installed or not)

Would anyone object to it being adjusted to

${MAKE} update 'DEPENDS_TARGET=package-install clean'

which should result in all the rebuilt packages and dependencies being
clean afterwards, but without the wasted effort. I've been running
with this for a few months

David