This makes it easier to install the headers, or to use them directly from
another software package with -I$(openflow)/include, without invading
the top-level include file namespace.
Move vlog option descriptions into a separate file lib/vlog.man that
is substituted into manpages.
Get rid of individual rules for substituting most files in favor of
a single suffix rule. Unfortunately this loses the (Emacs-specific)
read-only markings but it simplifies the makefiles.
Make "make" behave properly when these are changed by re-running
"configure", by putting their definitions into a generated file that
depends on Makefile.
Ben Pfaff