Show the replacement requirements

Instead of just blindly replacing the requirements without
logging the new replacement change it so that we log the original
and replacement requirement (which can be very useful for
debugging requirement problems).

Change-Id: I09ad966c427ce491963cf4a5e73ec3f8b92ed4cd
Only backup and replace requirement files if mutated

Change-Id: I710508a9416aa86fc585791edbcbd5d883e21f13