Package libshell: Information

- New utilities:
  + shell-run: New functions to scripts from directory.
  + shell-source: New functions to source shell code under some conditions.
- shell-quote changes:
  + Allow \t as delimiter.
- Other changes:
  + Protect IFS variable when 'set --' executing.

- Fix shell-var installation.

- New utilities:
  + shell-var: New functions to handle shell parameters.
- shell-quote changes:
  + Major changes in quote_shell_args().
  + Rewrite quote_shell_args() from scratch, to avoid the dangerous
    shell constructions.
  + Fix Usage for quote_shell_args.
  + Add quote_shell_args().
- shell-unittest changes:
  + Add default comment initialization.
- shell-args changes:
  + parse_common_option(): Option --quiet cancels option --verbose.
- Other changes:
  + Update COPYING.
  + UnitTest: Add tests for quote_shell_args() function.
  + shell_var_unquote(), string_quote_remove(): Fix "'" unquote
    for bash.