LDAP lookup of connection parameters

This patch for libpq allows you to enter an LDAP URL in pg_service.conf.
The URL will be queried and the resulting string(s) parsed for
keyword = value connection options.

The idea is to have connection information stored centrally on an LDAP
server rather than on the client machine.

On Windows the native library wldap32.dll is used, else OpenLDAP.
If --enable_thread_safety has been given, -lldap_r is appended to
PTHREAD_LIBS so that libpq will be linked against the tread safe
library.

There should probably also be a documentation patch for the --with-ldap
option of ./configure, but I didn't write it because it also belongs to
the
"LDAP Auth" patch.

I have added German translations for the new messages - how can I get
translations into other languages?

Yours,
Laurenz Albe