[backend] bs_worker: make sure that we don't run old code

This could happen when the worker was started from some other
directory than the statedir and the statedir had an up-to-date
copy of the worker code.

src/backend/bs_worker

@@ -3489,6 +3489,8 @@ sub periodic {
 
 
 # better safe than sorry...
+my $startworkercode = '?';
+$startworkercode = codemd5('.') if -e './bs_worker';
 chdir($statedir) || die("$statedir: $!\n");
 
 BSServer::deamonize(@ARGV) unless $oneshot;
@@ -3498,6 +3500,7 @@ $| = 1;
 # calculate code meta md5
 $workercode = codemd5('worker');
 $buildcode = codemd5('build');
+$workercode = $buildcode = '?' if $startworkercode ne $workercode;
 
 open(RUNLOCK, '>>', "$statedir/lock") || die("$statedir/lock: $!");
 flock(RUNLOCK, LOCK_EX | LOCK_NB) || die("worker is already running on $statedir!\n");