Fix small bug in tuple constructors
Fix small bug in tuple constructors

Ignore-this: a3e81a7e4a5e4208c1aaa46b506986f4
SFINAE now works properly for non-ranges.

darcs-hash:20150107101430-c9a90-9a3a4e049a0fdf82f516dbf9a12d2d0cdab478e3

rogiervd/range,rogiervd/range,rogiervd/range