Fix compiler warnings and make the code a bit clearer

The warnings are generated because GCC 4.2 didn't know of which type the
object from the array was, and it guessed that it was some object which
returns an NSString *, which cannot be cast to PTYTab * without warning.

PseudoTerminal.m

@@ -482,7 +482,8 @@ NSString *sessionsKey = @"sessions";
 {
     NSArray* items = [TABVIEW tabViewItems];
     for (int i = 0; i < [items count]; i++) {
-        if ([[items objectAtIndex:i] identifier] == aTab) {
+        NSTabViewItem *tabViewItem = [items objectAtIndex:i];
+        if ([tabViewItem identifier] == aTab) {
             return i;
         }
     }
@@ -2216,7 +2217,10 @@ NSString *sessionsKey = @"sessions";
         ([[PreferencePanel sharedInstance] hideTab] && ([TABVIEW numberOfTabViewItems] > 1 && [tabBarControl isHidden]))) {
         // Need to change the visibility status of the tab bar control.
         PtyLog(@"tabViewDidChangeNumberOfTabViewItems - calling fitWindowToTab");
-        PTYTab* firstTab = [[[TABVIEW tabViewItems] objectAtIndex:0] identifier];
+
+        NSTabViewItem *tabViewItem = [[TABVIEW tabViewItems] objectAtIndex:0];
+        PTYTab *firstTab = [tabViewItem identifier];
+
         if (wasDraggedFromAnotherWindow_) {
             // A tab was just dragged out of another window's tabbar into its own window.
             // When this happens, it loses its size. This is our only chance to resize it.