[v3] Rename a few testcases

[Paolo Carlini]

Hi,

I'm renaming a few testcases which actually are about alias declarations 
not typedefs.

Thanks,
Paolo.

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2014-10-14  Paolo Carlini  <paolo.carl...@oracle.com>

        * testsuite/20_util/add_lvalue_reference/requirements/typedefs.cc:
        Rename to alias_decl.cc.
        * testsuite/20_util/add_rvalue_reference/requirements/typedefs.cc:
        Likewise.
        * testsuite/20_util/common_type/requirements/typedefs-3.cc: Likewise.
        * testsuite/20_util/conditional/requirements/typedefs-2.cc: Likewise.
        * testsuite/20_util/decay/requirements/typedefs-2.cc: Likewise.
        * testsuite/20_util/enable_if/requirements/typedefs-2.cc: Likewise.
        * testsuite/20_util/make_signed/requirements/typedefs-3.cc: Likewise.
        * testsuite/20_util/make_unsigned/requirements/typedefs-3.cc:
        Likewise.
        * testsuite/20_util/remove_reference/requirements/typedefs.cc:
        Likewise.
        * testsuite/20_util/result_of/requirements/typedefs.cc: Likewise.
        * testsuite/20_util/underlying_type/requirements/typedefs-3.cc:
        Likewise.