nasty way to make versions unique

could be done better I'm sure

misc-scripts/assembly/ensembl_assembly_to_chain.pl

@@ -160,7 +160,18 @@ sub run_on_dba {
 sub get_liftover_mappings {
   my ($core_dba) = @_;
   my $mappings = $core_dba->get_MetaContainer()->list_value_by_key('liftover.mapping');
-  return [ map { $_ =~ /.+:(.+)#.+:(.+)/; [$1, $2] } @{$mappings} ];
+  my %unique_mappings;
+  for (@$mappings){
+      die "Can't parse mapping string for coord system version '$_'!\n"
+          unless /.+:(.+)#.+:(.+)/;
+      my $version_1 = $1;
+      my $version_2 = $2;
+      $unique_mappings{$version_1. ":". $version_2}++;
+  }
+  my @unique_mappings;
+  push @unique_mappings, [split(/:/, $_)]
+      for keys %unique_mappings;
+  return \@unique_mappings;
 }
 
 sub write_mappings {