* Introduces VMCache::CanWritePage() returning whether the given cache can

theoretically write the given page.
* page writer: Fixed the incorrect check whether a temporary page can be
  written by using the new CanWritePage().


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@30281 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vm_types.h

@@ -219,6 +219,7 @@ public:
 	virtual	status_t	WriteAsync(off_t offset, const iovec* vecs,
 							size_t count, size_t numBytes, uint32 flags,
 							AsyncIOCallback* callback);
+	virtual	bool		CanWritePage(off_t offset);
 
 	virtual	status_t	Fault(struct vm_address_space *aspace, off_t offset);