Make == for associative arrays test for equality, not identity.

_aaEq was added to runtime/internal/aaA.d which forwards to
TypeInfo_AssociativeArray.equals in genobj.d. On the codegen side, DtoAAEquals
was added to gen/aa.cpp and is called from EqualExp::toElem in gen/toir.cpp.

I assume that the frontend will produce an error if == is used on associative
arrays of different type.

This fixes DMD bug 1429.

runtime/internal/aaA.d

@@ -705,6 +705,11 @@ body
 }
 
 
+int _aaEq(AA aa, AA ab, TypeInfo_AssociativeArray ti)
+{
+    return ti.equals(&aa, &ab);
+}
+
 /***********************************
  * Construct an associative array of type ti from
  * length pairs of key/value pairs.

runtime/internal/genobj.d

@@ -47,6 +47,8 @@ private
     import util.string;
     import tango.stdc.stdio;  // : printf, snprintf;
     import tango.core.Version;
+    
+    import aaA;
 
     extern (C) void onOutOfMemoryError();
     extern (C) Object _d_allocclass(ClassInfo ci);
@@ -555,6 +557,29 @@ class TypeInfo_AssociativeArray : TypeInfo
     }
 
     // BUG: need to add the rest of the functions
+    
+    int equals(void *p1, void *p2)
+    {
+        AA aa = *cast(AA*)p1;
+        AA ab = *cast(AA*)p2;
+        
+        if (_aaLen(aa) != _aaLen(ab))
+            return 0;
+        
+        int equal = 1;
+        int eq_x(void* k, void* va)
+        {
+            void* vb = _aaIn(ab, key, k);
+            if (!vb || !value.equals(va, vb))
+            {
+                equal = 0;
+                return 1; // break
+            }
+            return 0;
+        }
+        _aaApply2(aa, key.tsize(), &eq_x);
+        return equal;
+    }
 
     size_t tsize()
     {