Remove STL algorithm tests from vector<> test

This removes the STL algorithm tests from the vector<> test.
Add variadic tuple support

This adds support for variadic tuples on C++11 compilers.
Add context error handler

This adds an error handler function which is invoked when an OpenCL
context encounters an error condition. The context error is converted
to a C++ exception containing the error information and thrown.
Add experimental copy_index_if() algorithm

This adds an experimental algorithm like copy_if() which copies
the index of the values for which predicate returns true instead
of the values themselves.
Add nth_element() algorithm

This adds an implementation of the nth_element() algorithm. For
now the algorithm is trivially implemented by calling sort().