Document new trigger-related forms of ALTER FOREIGN TABLE.

Oversight in commit 7cbe57c34dec4860243e6d0f81738cfbb6e5d069.
Back-patch to 9.4, where that commit first appeared.  In passing,
release-note the FDW API postcondition change from the same commit.
Make pg_service.conf sample LDIF more portable.

The aboriginal sample placed connection parameters in
groupOfUniqueNames/uniqueMember.  OpenLDAP, at least as early as version
2.4.23, rejects uniqueMember entries that do not conform to the syntax
for a distinguished name.  Use device/description, which is free-form.
Back-patch to 9.4 for web site visibility.
Install libpq DLL with $(INSTALL_SHLIB).

Programs need execute permission on a DLL file to load it.  MSYS
"install" ignores the mode argument, and our Cygwin build statically
links libpq into programs.  That explains the lack of buildfarm trouble.
Back-patch to 9.0 (all supported versions).