* gdb.base/a1-selftest.exp: Don't test "maint dump-me". That test

	* gdb.base/a1-selftest.exp: Don't test "maint dump-me".  That test
	was a vestige of the manual TESTSTRATEGY, and the purpose of it
	was to make sure that gdb can read a core file.  But (a) the "read
	the corefile" part didn't make it to a1-selftest.exp, we just
	delete the corefile after creating it, and (b) we test reading
	corefiles in corefile.exp anyway.  Also, this test left around a
	xgdb process on Solaris.

	* gdb.base/corefile.exp: Also test backtrace.