strategy is to leave alone the install targets sprinkled all over
the Makefiles and instead to two thigns:
(1) Define new INST_* variants of BINDIR, ETCDIR, MODULEDIR, etc.
that are the "final" installation locations, and thus may be
hardcoded into the program.
(2) Modify the definitions of BINDIR, ETCDIR, MODULEDIR, etc. to
point to $(DESTDIR)$(INST_*). These variables can be used in
the _install targets without any changes.
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