Bug 311 - Don't include performance.sgml ( 'man') file twice in the tar
Only include the libpq header directory OR the server header directory but not both

This addresses bug 315 where a debian install had libpq-dev 9.3 installed
and postgresql-server-dev 8.4 installed.  The libpq headers are in /usr/include/postgresql
but the server headers are in /usr/lib/postgresql/8.4/server.

configure checks were failing because we were pulling in a mixutre of headers
from both versions.  The only slony component that needs the server
headers are the backend functions and they shouldn't need to use libpq headers.

This patch sets CPPFLAGS as approriate for one or the other but not both
Use server includes for pgport when building slonik

When building with --with-pgport slonik needs to include port.h
port.h is normally found under the server include directory but
some distributions (ie debian libpq-dev) also include it in
/usr/include/postgresql

The fix for bug 315 removed the server include paths from
all client programs including slonik.  This went too far,
the actual issue with bug 315 was src/backend failing because
it pulled in the client headers.

If we are building with pgport we will pull in the server
include directories for slonik
fixing  Deadlock with application during minor version slony upgrade
fixing  Deadlock with application during minor version slony upgrade
Remove HAVE_POSIX_SIGNALS from config.h

Compiling slony against PG 9.4 gives compiler warnings because the
definition of HAVE_POSIX_SIGNALS has changed.  This is defined in pg_config
so we do not really need to redefine it in the config.h slony provides.

We leave the configure check in place to we just don't include it in
the header