better library clean

See README 1.27 log

  with the shared libraries instead of static, defaults to no
* build/lib-shared.mk: if LINK_BINS_DYNAMIC is set we create a symlink to
  the .so and .so.# file along with the .a and .la files
* build/lib.mk: make sure the above links get removed on clean target
* build/top.mk: add define for LINK_BINS_DYNAMIC
* tests/scripts/defines.sh: add export for LD_LIBRARY_PATH so that tests will
  run without requiring installation of libraries when we use --enable-dynamic
  (LD_LIBRARY_PATH is always set, since it can't really hurt).

  -lldap_r can now be implemented...

including use of ctime_r, gethostby*_r, etc..  Also reworked ldap_sort_entries
to be reentrant.
Need to add code to properly set LDAP_API_FEATURE_THREAD_SAFE.

  Updated to use libtool 1.2 (with FreeBSD3.0 a.out v. elf detection).
  Updated autoconf to 1.12 with sed patch (don't use stock 1.12).
  aclocal.m4 is built using automake's aclocal, v1.3.
  Updated mkdep to support libtool .lo files.
Updated automake provided macros for TERMIOS, STRTOD, MKTIME, PTRDIFF_T
Autoconf now checks to ensure C compiler supports ANSI C prototypes.
Updated make files templates.

Add basics of Kerberos detection.

Now to sort out configure enable/with options.