(f90-keywords-re): Added operator and result.

(f90-keywords-re): Added operator and result.
(f90-keywords-level-3-re): Added operator and result.
(f90-match-end, f90-looking-at-program-block-start): Fixed bug
with false matching in comments/strings.
(f90-looking-at-program-block-start, f90-imenu-generic-expression):
Added knowledge of pure and extrinsic subroutines.
(f90-abbrev-start): Fixed bug using next-command-event.
(f90-keywords-level-3-re): Added keyword "nullify".
(f90-else-like-re): Fixed indentation of case() statements.
(f90-font-lock-keywords-2): Changed highlighting of case() statements.