allow no-user-modification propagations if back-ldap is used for replication (i.e. updatedn is defined)

add administrative bind and proxyAuthz control to enable bound operations in distributed directories (need to manually #define LDAP_BACK_PROXY_AUTHZ and patches from ITS#2851 and ITS#2852)

instead of re-using other contexts.

All DN attrs are massaged, whether or not ENABLE_REWRITE is defined.
Use "dnAttr" rewriteContext for Add, Compare, & Modify.
Fixed ldap_back_compare.

consolidated into the Operation structure. All reply parameters
are consolidated into the new SlapReply structure. Most operations
now have identical call signatures... Changes are not #ifdef'd,
revert to -r NO_SLAP_OP_BLOCKS if necessary to back out.

they will be interleaved in LDAP*. Avoid setting any options on the handle.

to access the same LDAP* handle.

hence, s/LDAP_OPERATIONS_ERROR/LDAP_OTHER/