relscan_details.h

relscan.h is a bit of an unfortunate header because it requires a lot of
other headers to compile, and is also required by execnodes.h.  This
quick patch removes the struct definitions from that file, moving them
into a new relscan_details.h file; the reworked relscan.h does not need
any other header, freeing execnodes.h from needlessly including lots of
unnecessary stuff all over the place.  Only the files that really need
the struct definition include the new file, and as seen in the patch,
they are quite few.

execnodes.h is included by 147 backend source files; relscan_details.h
only 27.  So the exposure area is reduced considerably.  This patch also
modifies a few other backend source files to add one or both of genam.h
and heapam.h, which were previously included through execnodes.h.

This is probably missing tweaks for contrib/.  The following modules
would need to include relscan_details.h: sepgsql dblink pgstattuple
pgrowlocks.  I expect the effect on third-party modules to be much less
than by the htup_details.h change.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services