Supress printing very long plists in debug output
lockdown: Fix error in re-pairing when previous record became invalid

When connecting with an existing pair record failed we attempted to
pair again which generated a new host id but then connect after
successful pairing tried to use host id from the old record and
failed. Make sure we forget the old host id when re-pairing.
This also fixes a possible memory leak.
Remove obsolete prefix from debug messages in internal locking helpers
common: Remove obsolete symbol hiding macros from userpref module
debug: Fix symbol locality for linker so debug messages are printed again
debug: Fix linking failure on OS X by keeping debug level symbol internal

This change keeps the debug level symbol within the internal convenience
library and makes it accessible using an internal helper. This fixes
linking, prevents new exported symbols and finally allows proper control
of enabling debug messages.