more straightforward way to get string width for message window

macosx/MessageWindowController.m

@@ -182,10 +182,7 @@
         if (!fAttributes)
             fAttributes = [[[[column dataCell] attributedStringValue] attributesAtIndex: 0 effectiveRange: NULL] retain];
         
-        NSAttributedString * string = [[NSAttributedString alloc] initWithString:
-                                        [[fMessages objectAtIndex: row] objectForKey: @"Message"] attributes: fAttributes];
-        count = [string size].width / width;
-        [string release];
+        count = [[[fMessages objectAtIndex: row] objectForKey: @"Message"] sizeWithAttributes: fAttributes].width / width;
     }
     
     return [tableView rowHeight] * (float)(count+1);