Revive config_test.c

Move config-dependent code (recvwithttl) from net.c to mdp_net.c (new)

Move log-implementation-independent code from log.c to log_util.c (new)

Build config_test binary in Makefile
Deprecate RHIZOME_MANIFEST_ID_... in favour of RHIZOME_BUNDLE_ID_...
Consolidate Rhizome string parsing functions

Remove unused rhizome_str[n]_is_...() functions in favour of
str[n]_to_rhizome_..._t() functions

Ensure that all str_to_..._t() functions accept a NULL 'dst' pointer
so they can be used easily to validate strings
Add missing copyright/license comment blocks

Update a few existing copyright notices to reflect recent work