change to conversion operator of input_iterator_archetype::proxy so

as to not use the copy constructor of the value_type


[SVN r22184]

libs/concept_check

@@ -1 +1 @@
-Subproject commit cc25398b06629347a7f4d219bb23acc5cc90c7fc
+Subproject commit 061ed8019ad4cc1c86fdf76677a4c56430f30a02