Preserve old DataPack behavior when overwriting data (#848)

* Match old DataPack behavior when overwriting data

* Make RemoveItem more flexible

* Ditch implied RemoveItem behavior & asher fixes

* KyleS nits - but fixed before he says them

* Add back implicit behavior

* Update CDataPack.cpp

Committing to the spec.

* Update CDataPack.h

* fixup removing last item if explicitly requested

* Fix logic for accepting pack pos, rather than index

* Fixup IsReadable

* headache is over now

core/logic/CDataPack.cpp

@@ -223,3 +223,24 @@ void *CDataPack::ReadMemory(size_t *size) const
 
 	return ptr;
 }
+
+bool CDataPack::RemoveItem(size_t pos)
+{
+	if (!elements.length())
+	{
+		return false;
+	}
+
+	if (pos == static_cast<size_t>(-1))
+	{
+		pos = position;
+	}
+	if (pos >= elements.length())
+	{
+		return false;
+	}
+
+	elements.remove(pos);
+	--position;
+	return true;
+}