Replace @VAR@ with ${VAR} unconditionally in scripts, even if they
values are empty. This will allow for fall-through to using the
pkgtasks hard-coded defaults, usually found by searching the PATH
contents, and it avoids having ugly "@VAR@" in the generated
scripts.
@TYPE1INST@ should be replaced with ${TOOLS_PATH.type1inst}.
Before this change, the sed(1) script being generated was not
replaced @TYPE1INST@ at all, and instead generating a no-op
substitution pattern for TTMKFDIR.
A full dependency on the "pkgtasks" package will be added if a
non-empty data file is generated by the framework.
This framework is not yet hooked into bsd.pkg.mk, pending some
other changes.
