removed a residual (pre autocalc of batchsize from runtime statistics)

design element in Worker::batch_size
- old design: setting the batch_size for a worker changed the batch_size for
  all workers by updating the analysis_stats.batch_size of the corresponding
  analysis. Although this code was never triggered in the current system, it
  could have caused potential problems for future developers.
Now setting the batch_size explicitly for a worker only effects the
batch_size for that Worker instance. If it has not been set, the Worker pulls
the batch_size from the analysis_stats record and optionally autocalcs from
avg_msec_per_job if the batch_size<=0.

modules/Bio/EnsEMBL/Hive/Worker.pm

@@ -339,17 +339,23 @@ sub cleanup_worker_process_temp_directory {
 
 =cut
 
+sub set_worker_batch_size {
+  my $self = shift;
+  my $batch_size = shift;
+  if(defined($batch_size)) {
+    $self->{'_batch_size'} = $batch_size;
+  }
+}
+
 sub batch_size {
   my $self = shift;
-  
+
   my $stats = $self->analysis->stats;
   my $batch_size = $stats->batch_size;
-  if(@_) {
-    $batch_size = shift;
-    $stats->batch_size($batch_size);
-    $stats->update;
-  }  
-  
+  if(defined($self->{'_batch_size'})) {
+    $batch_size = $self->{'_batch_size'};
+  } 
+    
   if(($batch_size <= 0) and ($stats->avg_msec_per_job)) {
     $batch_size = int(120000 / $stats->avg_msec_per_job); # num jobs in 120 secs
   }

scripts/runWorker.pl

@@ -171,11 +171,10 @@ else {
 }
 
 if($self->{'batch_size'}) {
-  $worker->batch_size($self->{'batch_size'});
+  $worker->set_worker_batch_size($self->{'batch_size'});
 }
 if($self->{'job_limit'}) {
   $worker->job_limit($self->{'job_limit'});
-  $worker->batch_size($self->{'job_limit'});
   $worker->life_span(0);
 }
 if($self->{'lifespan'}) {