Move mutexes to end of structs, so libldap can ignore them

With gcc, declare debug_already_initialized() as 'noinline' so
its deliberate uninitialized access stays inside the function and
valgrind can ignore it there.

connection_<first/next>() takes a ber_socket_t *index, not int*.

Code comments belong in the code, not in commit messages.

Only wait out already-started pauses, not pause reqests.
ltp_pause now says whether a pause is requested or has started.

This reduces the chance that slapd:send_ldap_ber() will start
a pause in the middle of an operation.

Track allocations and invalid accesses to freed tmp pages.

Fix for failure when committing a txn that is a child of
some parent txn.

Don't compare cursors that aren't deep enough to match the
current cursor.

Use PERL_SYS_INIT3() after all.  There appears to be no correct
way to do this, so we should as least follow the documentation.

Partial revert of 9e00b6cc:connection.c.

Subject: ITS#7111

Additional fix for a66fb163

Should not do anything in tool mode.

Originally, overlays were not supposed to take effect in tool mode.
Apparently that's no longer the case...