Use <tab> as indentation character in file lists

Mostly for consistency with the rest of the file.

CMakeLists_files.cmake

@@ -41,7 +41,7 @@ list (APPEND MAIN_SOURCE_FILES
 	opm/core/grid/cpgpreprocess/uniquepoints.c
 	opm/core/io/eclipse/EclipseGridInspector.cpp
 	opm/core/io/eclipse/EclipseWriter.cpp
-        opm/core/io/eclipse/EclipseReader.cpp
+	opm/core/io/eclipse/EclipseReader.cpp
 	opm/core/io/eclipse/EclipseWriteRFTHandler.cpp
 	opm/core/io/eclipse/writeECLData.cpp
 	opm/core/io/OutputWriter.cpp
@@ -158,7 +158,7 @@ list (APPEND MAIN_SOURCE_FILES
 # find tests -name '*.cpp' -a ! -wholename '*/not-unit/*' -printf '\t%p\n' | sort
 list (APPEND TEST_SOURCE_FILES
   tests/test_writenumwells.cpp
-        tests/test_readWriteWellStateData.cpp
+	tests/test_readWriteWellStateData.cpp
 	tests/test_EclipseWriter.cpp
 	tests/test_EclipseWriteRFTHandler.cpp
 	tests/test_compressedpropertyaccess.cpp
@@ -291,7 +291,7 @@ list (APPEND PUBLIC_HEADER_FILES
 	opm/core/io/eclipse/EclipseGridInspector.hpp
 	opm/core/io/eclipse/EclipseUnits.hpp
 	opm/core/io/eclipse/EclipseWriter.hpp
-        opm/core/io/eclipse/EclipseReader.hpp
+	opm/core/io/eclipse/EclipseReader.hpp
 	opm/core/io/eclipse/EclipseWriteRFTHandler.hpp
 	opm/core/io/eclipse/writeECLData.hpp
 	opm/core/io/OutputWriter.hpp