better autoconf tcp wrapper test (ITS#1544)

[china@thewrittenword.com]

Full_Name: Albert Chin-A-Young
Version: 2.0.21
OS: Solaris
URL: ftp://ftp.thewrittenword.com/outgoing/pub/openldap-2.0.21-3.patch
Submission from: (NULL) (64.32.187.114)


Attached is a better TCP wrapper autoconf test. It has the following
advantages:
  1. Doesn't use internal autoconf names like $ac_cv_header_tcpd_h
  2. AC_TRY_LINK rather than AC_TRY_COMPILE to successfully test
     for existence of tcp library functions.
  3. Doesn't blindly add -lnsl but adds it temporarily to $LIBS if
     the AC_TRY_LINK test fails without -lnsl in $LIBS (or whatever
     the default $LIBS is).

Patch at:
  ftp://ftp.thewrittenword.com/outgoing/pub/openldap-2.0.21-3.patch