Update synchronization annotations for struct vm_page.  Add a comment explaining how the setting of PG_WRITEABLE is synchronized.
Update synchronization annotations for struct vm_page.  Add a comment
explaining how the setting of PG_WRITEABLE is synchronized.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase