mingw configure fix, host: fix, compiler warnings in ldap.c

                                  Changelog

Daniel (6 February 2004)

- Andrés García made the configure script find gethostbyname() fine when run

  with mingw on windows.

- Modifed the ldap code to use proper function pointers all over (instead of

  mixed data and function pointers) to work-around the picky MIPSPro compiler

  warnings.

- A custom Host: header is only considered if the request is not made by

  following a location. After discussions with Tim Baker.

Daniel (5 February 2004)

- The libz part of the configure script now only set the two libz-related

  define HAVE_ZLIB_H and HAVE_LIBZ if both the lib and the header is found.