ITS#7761 bail out of search if config is pausing
ITS#7762 shortcut NULL RDNs
ITS#6758 Add SLAP_OP() &co, contrib:wrap_slap_ops.

Add framework for debug macros SLAP_OP(), slap_be_op(),
slap_bi_op() around LDAP-operation backend calls.

contrib/slapd-tools/wrap_slap_ops converts code to use them.

Code compiles as before by default.  #define USE_RS_ASSERT
enables debugging, $NO_RS_ASSERT tweaks it. See slapd/result.c.
ITS#6758 Rewrite code for contrib:wrap_slap_ops.

Tweak slapd code so wrap_slap_ops can process it: Use pointers
BackendInfo *bi instead of array "func" = &bi->bi_op_bind. In
slapo-chain, keep a slap_operation_t instead of a function ptr.