Remove unused variable(#1)
Fix for new Emacs(24.3 or higher)

We check that `isearch--state-string` is defined,
because its function is introduced Emacs 24.3.

Emacs 24.2 or lower users should use isearch-string-state
Fix for obsoleted variables(#1)

Variable `file-coding-system-*` is obsoleted and deleted long time ago.
We should use `buffer-file-coding-system`.
Merge pull request #4 from emacs-jp/fix_bytecompile-2

Fix byte compile problem