Handle PERM_EXPORT in LLPermissions.

This moves all export test code to where it belongs:
in LLPermissions.

Added LLPermissions::allowExportBy, next to
allowModifyBy, allowCopyBy and allowMoveBy.
Then changed all code to use this call.

Because LLPermissions is part of llinventory, I had
to add a proxy for LFSimFeatureHandler.
Added a new class LFSimFeatureHandlerInterface that can be
used by LLPermissions to check simulator features by
accessing the LFSimFeatureHandler singleton.

Several parts of the code ignored the PERM_EXPORT but
and still did demand that things are full perm next
to being a creator. This has now changed the export
rules are the same for everything as they were for mesh:
you need to be the owner and the creator for every element
that is exported (not just the root prim, of course).

Export rules can now be easily made a function on
simulator features. If different rules apply for different
types (wearables, objects, mesh etc) then an extra variable
indicating the type will have to be passed though.

indra/newview/lfsimfeaturehandler.h

@@ -19,6 +19,7 @@
 #define LFSIMFEATUREHANDLER_H
 
 #include "llsingleton.h"
+#include "llpermissions.h"
 
 template<typename Type>
 class SignaledType
@@ -45,7 +46,7 @@ private:
 	Type mValue;
 };
 
-class LFSimFeatureHandler : public LLSingleton<LFSimFeatureHandler>
+class LFSimFeatureHandler : public LFSimFeatureHandlerInterface, public LLSingleton<LFSimFeatureHandler>
 {
 protected:
 	friend class LLSingleton<LFSimFeatureHandler>;
@@ -59,7 +60,7 @@ public:
 	boost::signals2::connection setSupportsExportCallback(const boost::signals2::signal<void()>::slot_type& slot);
 
 	// Accessors
-	bool simSupportsExport() const { return mSupportsExport; }
+	/*virtual*/ bool simSupportsExport() const { return mSupportsExport; }
 
 private:
 	// SignaledTypes