fixed the type of iterator uses in MWWorld::Store

The containers type used to declare some iterators was not an exact match for the type of the container the iterator was being initialized from. This was causing build failure on windows.

apps/openmw/mwworld/store.hpp

@@ -475,7 +475,7 @@ namespace MWWorld
             cell.mData.mX = x, cell.mData.mY = y;
 
             std::pair<int, int> key(x, y);
-            std::map<std::pair<int, int>, ESM::Cell>::const_iterator it = mExt.find(key);
+            DynamicExt::const_iterator it = mExt.find(key);
             if (it != mExt.end()) {
                 return &(it->second);
             }
@@ -493,7 +493,7 @@ namespace MWWorld
             cell.mData.mX = x, cell.mData.mY = y;
 
             std::pair<int, int> key(x, y);
-            std::map<std::pair<int, int>, ESM::Cell>::const_iterator it = mExt.find(key);
+            DynamicExt::const_iterator it = mExt.find(key);
             if (it != mExt.end()) {
                 return &(it->second);
             }
@@ -534,7 +534,7 @@ namespace MWWorld
 
         void setUp() {
             //typedef std::vector<ESM::Cell>::iterator Iterator;
-            typedef std::map<std::pair<int, int>, ESM::Cell>::iterator ExtIterator;
+            typedef DynamicExt::iterator ExtIterator;
             typedef std::map<std::string, ESM::Cell>::iterator IntIterator;
 
             //std::sort(mInt.begin(), mInt.end(), RecordCmp());