Interval cosine function broken

Code to reproduce:

```
#include

using boost::numeric::interval;
using namespace boost::numeric::interval_lib;

int main()
{
auto x = cos(interval(2.3));
return 0;
}
```

Error message:

```
g++-7 -Wall -Wextra -Wfatal-errors -fext-numeric-literals main.cpp -o main.x -pthread
main.cpp: In function 'int main()':
main.cpp:8:10: warning: variable 'x' set but not used [-Wunused-but-set-variable]
auto x = cos(interval(2.3));
^
In file included from ../numeric/interval/include/boost/numeric/interval.hpp:30:0,
from main.cpp:1:
../numeric/interval/include/boost/numeric/interval/transc.hpp: In instantiation of 'boost::numeric::interval boost::numeric::cos(const boost::numeric::interval&) [with T = double; Policies = boost::numeric::interval_lib::policies, boost::numeric::interval_lib::checking_strict >]':
main.cpp:8:39: required from here
../numeric/interval/include/boost/numeric/interval/transc.hpp:73:18: error: 'boost::numeric::interval_lib::policies, boost::numeric::interval_lib::checking_strict >::rounding {aka struct boost::numeric::interval_lib::rounded_math}' has no member named 'cos_down'; did you mean 'conv_down'?
return I(rnd.cos_down(u), rnd.cos_up(l), true);
~~~~^~~~~~~~
conv_down
compilation terminated due to -Wfatal-errors.
make: *** [main.x] Error 1
```

Compiled against a fresh clone.