list.exp: Avoid hardcoding line numbers.

list.exp: Avoid hardcoding line numbers.

The previous patch actually wasn't the first time I had to update line
numbers in this file.

This avoids hard coding line numbers, hopefully making the next time a
little easier.

Tested on x86_64 Fedora 17.

gdb/testsuite/
2013-03-28  Pedro Alves  <palves@redhat.com>

	* gdb.base/list.exp (last_line): New global.
	(last_line_re): New global.
	(test_listsize, test_list_function, test_list_forward)
	(test_repeat_list_command, test_list_range)
	(test_list_filename_and_function): Use them.
	* gdb.base/list0.c: Comment the last line of the file with "last
	line".