ecpg: Don't link compatlib with libpq

It doesn't actually use libpq.  But we need to keep libpq in the
CPPFLAGS for building, because compatlib uses ecpglib.h which uses
libpq-fe.h, but we don't need to refer to libpq for linking.

reviewed by Tom Lane
Add pkg-config files for libpq and ecpg libraries

This will hopefully be easier to use than pg_config for users who are
already used to the pkg-config interface.  It also works better for
multi-arch installations.

reviewed by Tom Lane
Ignore extra subquery outputs in set_subquery_size_estimates().

In commit 0f61d4dd1b4f95832dcd81c9688dac56fd6b5687, I added code to copy up
column width estimates for each column of a subquery.  That code supposed
that the subquery couldn't have any output columns that didn't correspond
to known columns of the current query level --- which is true when a query
is parsed from scratch, but the assumption fails when planning a view that
depends on another view that's been redefined (adding output columns) since
the upper view was made.  This results in an assertion failure or even a
crash, as per bug #8025 from lindebg.  Remove the Assert and instead skip
the column if its resno is out of the expected range.
Update release notes for changes through today.
Revert "ecpg: Don't link compatlib with libpq"

This reverts commit 3780fc679cc428c1f211e1728c4281ca15e9746b.

HP-UX didn't like it.  There would probably be a way to fix that, but
since the net effect of all of this is zero because ecpg ends up using
libpq anyway, it's not worth bothering further.