Series to allow a "const" file_operations struct

Hi,

this series allows drivers to have "const" file_operations, by making
the f_ops field in the inode const. This has another benefit, there have
been several bugs where code accidentally wrote to the ->f_ops
structure, forgetting that it's a shared structure. One of those bugs
got fixed in november for example (as a result of these patches),
another one is fixed in this series. 

Greetings,
   Arjan van de Ven