Bug 871473: New code hook "before_read" in Migrate.pm

Bugzilla/Migrate.pm

@@ -153,6 +153,7 @@ sub do_migration {
     }    
     $dbh->bz_start_transaction();
 
+    $self->before_read();
     # Read Other Database
     my $users    = $self->users;
     my $products = $self->products;
@@ -544,6 +545,7 @@ sub write_config {
 sub after_insert  {}
 sub before_insert {}
 sub after_read    {}
+sub before_read   {}
 
 #############
 # Inserters #
@@ -1147,6 +1149,11 @@ and yet shouldn't be added to the initial description of the bug when
 translating bugs, then they should be listed here. See L</translate_bug> for
 more detail.
 
+=head2 before_read
+
+This is called before any data is read from the "other bug-tracker".
+The default implementation does nothing.
+
 =head2 after_read
 
 This is run after all data is read from the other bug-tracker, but