Minor update to build opm-core with current ert master

This PR consist of two commits:

1. a6e3bbd6109826988c4fd24973f7c91d46c1e491: the ert function ecl_util_fmt_file() has changed signature slightly; with this commit opm-core compiles against ert/master.
2. 1281d17b60767736271c15f4f032d58994f1363e: the restart files written by writeECLData() are now by default unformatted. The formatted/unformatted status should probably be an input flag, and calls should be aligned between this function and the EclipseGridParser::saveEGRID_INIT() function. The latter does not seem to be called from opm-core.