Use testing iterator wrappers to ensure that algorithms support their stated requirements

Since InputIterators can't be dereferenced multiple times we shouldn't implement algorithms like copy_if(first, last, output, pred) with copy_if(first, last, first, output, pred).

In general the unit tests should check InputIterator semantic correctness.

Forwarded from http://code.google.com/p/thrust/issues/detail?id=419