Implement globbing and enhance cat to accept multiple files.

* bzrlib/tests/test_script.py:
(TestSyntax.test_command_with_single_quoted_param,
TestSyntax.test_command_with_double_quoted_param): Quotes are left
in place during command splitting.
(TestArgumentProcessing): Test quote removal and globbing.
(TestCat.test_cat_files_to_file): Cat accepts multiple files now.

* bzrlib/tests/script.py:
(split): Delay quote removal until the command is ready to be
executed.
(ScriptRunner._pre_process_args): Globbing should happen just
before command execution, which imply that quotes removal should
happen at the same time.
(ScriptRunner.run_command): Process arguments for quote and
globbing just before execution or globbing will not be correct.
(ScriptRunner.do_cat): Allow multiple files to be specified.