list.exp: Adjust "set listsize -1" to current test source's real line count.

list.exp: Adjust "set listsize -1" to current test source's real line count.

The "set listsize -1" test in list.exp can't work correct anymore
nowadays, because the test's source files grew over time, and this
particular test was never updated.

This fixes it in the obvious way.

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

	* gdb.base/list.exp (test_listsize): Adjust test to make sure we
	list the whole file.