abiword build failed, cairo not buildlinked

["Jeremy C. Reed" <reed%reedmedia.net@localhost>]

Trying to build cairo failed as I had cairo-1.5.12 installed.

cairo was recently updated and buildlink3.mk changed to:

-BUILDLINK_API_DEPENDS.cairo+=  cairo>=1.0.0nb2
+BUILDLINK_API_DEPENDS.cairo+=  cairo>=1.6.4

But my gtk2+ and pango packages were good enough so cairo was not updated 
causing the abiword build to fail because cairo was not buildlinked.

The pkgsrc guide says:

"The situation that requires increasing the dependency listed in 
BUILDLINK_API_DEPENDS.pkg after a package update is when the API or 
interface to the header files change.

"In this case, BUILDLINK_API_DEPENDS.pkg should be adjusted to require at 
least the new package version. In some cases, the packages that depend on 
this new version may need their PKGREVISIONs increased and, if they have 
buildlink3.mk files, their BUILDLINK_API_DEPENDS.pkg adjusted, too. This 
is needed so pkgsrc will require the correct package dependency and not 
settle for an older one when building the source."

Following this documented policy, buildlink3.mk should have been adjusted 
for pango and gtk2+ (and maybe others too).

I don't understand the above though. Why does the buildlink3 system do 
this? I'd prefer that it started to build and fail on install for the 
needed package as needed by BUILDLINK_API_DEPENDS.pkg.

Does anyone care about this? Or do you all remove all packages before 
updating? Or only build packages in clean location?