Log Message:
0.23: Pass PKGNAME_REQD to make operations.

Set PKGNAME_REQD to give underlying make processes a chance to set
options derived from the package name.  For example, the appropriate
version of Python can be derived from the package name (so, when
building py25-foo, use python-2.5, not python-2.6).   Specifically,
  MAKE_SET_VARS='PKGNAME_REQD=${pkg}-*'

From Alan Barret via pkgsrc-users@.