Previously the regex issued warning for all files containing ".[0-9]*." in the name
in the output directory. That was too general and created more warnings than we wanted.
The regex we are using might also consider a file named bla.2.blub.
In that case it is not nice to throw an exception. Instead we print
a message to std::cerr.
This is currently still happening due to the implementation of
OPM_THROW whenever the linear solver does not converge. This
happens quite often and we might not want to get overwhelmed by
the issue tracker.
