Use minimum 5 digits for step numbers in output file names.

Was 3 digits, created trouble for certain scripts reading
the files when more than 1000 steps were taken.
Add ert-detecting macro for building with ert support.

This is primarily intended for enabling eclipse-format output from simulators.
Also add missing header to Makefile.am, to fix 'make distcheck'.
Suppress output of multi-cell-block sizes and #iterations.
Add eclipse output to simulator.

Note: so far only for incompressible fluid simulator.
Merge pull request #6 from atgeirr/master

Improved output facilities