Reduce the number of DN normalization
    
    . Adding SLAPI_TARGET_SDN as well as its macros, SLAPI_SEARCH_TARGET_
      SDN SLAPI_ADD_TARGET_SDN, SLAPI_MODIFY_TARGET_SDN, etc.
    . Adding SLAPI_MODRDN_NEWSUPERIOR_SDN.
    . SLAPI_TARGET_DN and SLAPI_MODRDN_NEWSUPERIOR are kept for the back-
      ward compatibility.  But they are marked as deprecated.  They are
      pointing dn in SLAPI_TARGET_SDN and SLAPI_MODRDN_NEWSUPERIOR_SDN,
      respectively.
    . slapi_pblock_set(.., SLAPI_TARGET_DN/SLAPI_MODRDN_NEWSUPERIOR, dn)
      takes dn string and reset Slapi_DN to SLAPI_TARGET_SDN/SLAPI_MODRDN_
      NEWSUPERIOR_SDN.
    . slapi_pblock_get(.., SLAPI_TARGET_DN/SLAPI_MODRDN_NEWSUPERIOR, &dn)
      retrieves dn out of SLAPI_TARGET_SDN/SLAPI_MODRDN_NEWSUPERIOR_SDN.
    . Replacing slapi_dn_normalization_ext call with generating Slapi_DN
      APIs (e.g., slapi_sdn_new_dn_...) as much as possible and stash it
      in pblock using SLAPI_TARGET_SDN.
    . When a normalized DN string is needed, get it using slapi_sdn_get_[n]dn
      from the stashed Slapi_DN.
    . Introduced a new field "udn" to Slapi_DN.
      "udn" is an original DN.
      "dn" is its normalized DN.
      "ndn" is its case-lowered normalized DN.
      Note: slapi_sdn_get_ndn_len represents the length of the normalized
      DN, which is "dn" as well as "ndn".  Thus, instead of calling strlen
      for the normalized dn, using slapi_sdn_get_ndn_len, as much as possible.
    . Taking advantage of the knowledge of the stage of the DN, call the
      most efficient DN creating API (e.g., slapi_sdn_new_dn_... vs.
      slapi_sdn_new_normdn_... vs. slapi_sdn_new_ndn_...)
    
    Others
    . Replacing inefficient array assignment with memset (acl.c) and
      memcpy (idl_common.c).
    . Fixing invalid memory access in LASDnsBuild (lib/libaccess/lasdns.cpp).
    . Fixing compiler warnings.
    
    Reviewed by rmeggins@redhat.com (Thank you, Rich!!)