c++: auto and dependent member name [PR105734]

In r12-3643 I improved our handling of type names after . or -> when
unqualified lookup doesn't find anything, but it needs to handle auto
specially.

	PR c++/105734

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_postfix_dot_deref_expression): Use typeof
	if the expression has auto type.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/auto57.C: New test.