We added code to allow a few spurious failures, but it didn't unmark
the request running.
IRC user 'mlz' (@molxyz) provided logs from his stuck-at-old-block lightningd:
lightningd(31981): Adding block 1261159: 00000000da3890ccd0f313a74fccfd4789654b496836da5c28a8d2ad28852264
lightningd(31981): Adding block 1261160: 00000000f70938a33aecbdd7b047cb5cf5b095ea4770c1335acf1859bad1e767
lightningd(31981): bitcoin-cli -testnet estimatesmartfee 2 CONSERVATIVE exited with status 1
Fixes: #749
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>