- Modified ANSI label code to preserve any ANSI label

- Modified ANSI label code to preserve any ANSI label
  already found by skipping over it rather than rewriting
  it.
- Split the ANSI label code into ansi_label.c
- Do not let user relabel an ANSI labeled tape.
- Applied a patch for the console help command supplied
  in a bug report.
- Added some new dev methods. Most notably was
  set_eof(), which handles setting all the dev variables
  when an EOF is just read. This is now used most everywhere
  in the code.

git-svn-id: https://bacula.svn.sourceforge.net/svnroot/bacula/trunk@1820 91ce42f0-d328-0410-95d8-f526ca767f89