Make anyone importing DIALS aware of !2.7 support
Make anyone importing DIALS aware of !2.7 support

Warning is only shown on first import, and can be silenced in Python 2.7 with

import warnings
with warnings.catch_warnings():
    warnings.simplefilter("ignore")
    import dials

cf. #1175

dials/dials,dials/dials,dials/dials,dials/dials,dials/dials