New files have been added to this directory, but not listed here.
Repair.

Now that we have src/common/ for code shared between frontend and backend,
we can get rid of (most of) the klugy ways that the keyword table and
keyword lookup code were formerly shared between different uses.
This is a first step towards a more general plan of getting rid of
special-purpose kluges for sharing code in src/bin/.

I chose to merge kwlookup.c back into keywords.c, as it once was, and
always has been so far as keywords.h is concerned.  We could have
kept them separate, but there is noplace that uses ScanKeywordLookup
without also wanting access to the backend's keyword list, so there
seems little point.

ecpg is still a bit weird, but at least now the trickiness is documented.

I think that the MSVC build script should require no adjustments beyond
what's done here ... but we'll soon find out.

All expression nodes now have an explicit output-collation field, unless
they are known to only return a noncollatable data type (such as boolean
or record).  Also, nodes that can invoke collation-aware functions store
a separate field that is the collation value to pass to the function.
This avoids confusion that arises when a function has collatable inputs
and noncollatable output type, or vice versa.

Also, replace the parser's on-the-fly collation assignment method with
a post-pass over the completed expression tree.  This allows us to use
a more complex (and hopefully more nearly spec-compliant) assignment
rule without paying for it in extra storage in every expression node.

Fix assorted bugs in the planner's handling of collations by making
collation one of the defining properties of an EquivalenceClass and
by converting CollateExprs into discardable RelabelType nodes during
expression preprocessing.

recent proposal.  As proof of concept, remove knowledge of Params from the
core parser, arranging for them to be handled entirely by parser hook
functions.  It turns out we need an additional hook for that --- I had
forgotten about the code that handles inferring a parameter's type from
context.

This is a preliminary step towards letting plpgsql handle its variables
through parser hooks.  Additional work remains to be done to expose the
facility through SPI, but I think this is all the changes needed in the core
parser.