Kernel: Invalidate file-backed VMO's when inodes are written.

The current strategy is simply to nuke all physical pages and force
reload them from disk. This is obviously not optimal and should eventually
be optimized. It should be fairly straightforward.

Kernel/FileSystem.h

@@ -111,6 +111,8 @@ public:
 protected:
     Inode(FS& fs, unsigned index);
     void set_metadata_dirty(bool b) { m_metadata_dirty = b; }
+    void inode_contents_changed(off_t, size_t, const byte*);
+    void inode_size_changed(size_t old_size, size_t new_size);
 
     mutable Lock m_lock;