This commit fixes an issue where BIP86 addresses were not being
discovered during wallet recovery/rescan operations.
The root cause was that init_txfilter() only populated the transaction
filter with BIP32-derived keys, preventing lightningd from recognizing
BIP86 UTXOs during blockchain scans. Now both BIP32 and BIP86 derived
scripts are included in the filter when BIP86 derivation is enabled.
This ensures that wallets restored from BIP39 mnemonics can properly
discover and display previously funded BIP86 addresses without requiring
manual address generation first.
[ We also move the slightly-lost comment about libbacktrace so it is
where we actually include <backtrace.h> --RR ]
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