improve limits handling and consistency; return "Admin limit exceeded" instead of "Unwilling to perform"

- implement pagedResults abandon by setting size=0
- misc code cleanup

LDAP Control Extension for Simple Paged Results Manipulation

contributed by Lynn Moss <lynnmoss@us.ibm.com> (ITS#2189)

applied with changes.

Converted ch_malloc and ch_calloc calls to SLAP_MALLOC and SLAP_CALLOC.

Converted ch_malloc and ch_calloc calls to SLAP_MALLOC and SLAP_CALLOC.

Converted ch_malloc and ch_calloc calls to SLAP_MALLOC and SLAP_CALLOC.

Converted ch_calloc and ch_malloc calls to SLAP_CALLOC and SLAP_MALLOC.

and autoconf); #include "ac/string.h" instead of <string.h>