Leave platform-specific type in operator def.n

The property get/set sugar for numerical indices has to stay platform-
agnostic. That is, we cannot use `uint32_t`, but must instead use `int`
in the operator definition, because `int` resolves exactly on both
32-bit and 64-bit platforms.

Fixes: nodejs#337

napi-inl.h

@@ -783,8 +783,8 @@ inline Object::PropertyLValue<std::string> Object::operator [](const std::string
   return PropertyLValue<std::string>(*this, utf8name);
 }
 
-inline Object::PropertyLValue<uint32_t> Object::operator [](uint32_t index) {
-  return PropertyLValue<uint32_t>(*this, index);
+inline Object::PropertyLValue<int> Object::operator [](int index) {
+  return PropertyLValue<int>(*this, index);
 }
 
 inline Value Object::operator [](const char* utf8name) const {
@@ -795,7 +795,7 @@ inline Value Object::operator [](const std::string& utf8name) const {
   return Get(utf8name);
 }
 
-inline Value Object::operator [](uint32_t index) const {
+inline Value Object::operator [](int index) const {
   return Get(index);
 }
 

napi.h

@@ -395,8 +395,8 @@ namespace Napi {
     );
 
     /// Gets or sets an indexed property or array element.
-    PropertyLValue<uint32_t> operator [](
-      uint32_t index /// Property / element index
+    PropertyLValue<int> operator [](
+      int index /// Property / element index
     );
 
     /// Gets a named property.
@@ -411,7 +411,7 @@ namespace Napi {
 
     /// Gets an indexed property or array element.
     Value operator [](
-      uint32_t index ///< Property / element index
+      int index ///< Property / element index
     ) const;
 
     /// Checks whether a property is present.