is a new target "show-all" that fits to the existing "debug",
"show-tools", "show-vars" targets. It prints a list of the variables
that make up the public interface to pkgsrc. Running this target is
especially useful if you want to do some things, you know that they must
have been implemented but you don't know what it is called. It also
shows the "class" of a variable (user-defined, package-defined,
system-defined).
Moved the changes-entry target to misc/developer.mk. To save some time,
that file is only included when PKG_DEVELOPER is defined.
Moved the build-defs-message target to misc/show.mk and renamed it to
show-build-defs, since almost all other *-message targets just print a
single line.
