ObjectiveC: add "objc" as extensions

objc is used as name of major mode for ObjectiveC in emacs.
To choose a proper language parser from  a mode line, -*- objc -*-,
ctags must know "objc" means ObjectiveC.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
ada: handle an empty file properly

With command line "ctags --language-force=ada Test/ocaml_empty.ml" ctags
crashes. This patch fixes this bug.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>