More convar insanity

1) Added natives: HookConVarChange(), UnhookConVarChange(), and GetConVarName()
2) Fixed bug(s) where ConVar handles were being created when they didn't need to be
3) Fixed bug where convars not created by SourceMod would be unregistered

--HG--
extra : convert_revision : svn%3A39bc706e-5318-0410-9160-8a85361fbb7c/trunk%40471

public/sourcepawn/sp_vm_api.h

@@ -224,7 +224,7 @@ namespace SourcePawn
 	class IPluginContext
 	{
 	public:
-		/** Virtual destructr */
+		/** Virtual destructor */
 		virtual ~IPluginContext() { };
 	public:
 		/** 
@@ -265,7 +265,7 @@ namespace SourcePawn
 		virtual IPluginDebugInfo *GetDebugInfo() =0;
 
 		/**
-		 * @brief Allocs memory on the secondary stack of a plugin.
+		 * @brief Allocates memory on the secondary stack of a plugin.
 		 * Note that although called a heap, it is in fact a stack.
 		 * 
 		 * @param cells			Number of cells to allocate.