arrays/vector: little correction on = std::vector

- forgot the borrowed flag.
simple consequence of the weak view change.
uility : add foreach_enumerate

- to be tested
gf : add nearest_point for krylov

To be cleaned, it is redundant.
I put it here to make the krylov app compile properly
utility : add tuple_serialize code
cmake: add macro to fix rpath to triqs install

- to be tested on mac
arrays: fix a missing include in eigenelements
utility : add printing of a tuple

- << tuple now works, with a default version.
Useful for debugging