restructure things so that every file has its own openfilestruct, and so

restructure things so that every file has its own openfilestruct, and so
that the values in it are used directly instead of being periodically
synced up with the globals; accordingly, remove the globals; this
changes pretty much every function

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2835 35c25a1d-7b9e-4130-9fde-d3aeb78583b8