Importing files with different casing in base name and extension would fail when
using libecl summary reader. E.g "norne_atw2013.SMSPEC" would fail since libecl
forces the extension to be lower case even though it is given the actual extension.
Removing the lowercasing allows more flexibility in the file naming.
The problem only occurs when the libecl summary reader is used, the opm-common
can already import these files.
Fixes#10720.
Fixes#10617.