[partition] Be more verbose about default file-system settings

- Log the type that is configured
 - Document that this is a delicate setting, case-sensitive and
   dependent on KPMCore.

src/modules/partition/gui/PartitionViewStep.cpp

@@ -574,6 +574,8 @@ PartitionViewStep::setConfigurationMap( const QVariantMap& configurationMap )
     QString defaultFS = CalamaresUtils::getString( configurationMap, "defaultFileSystemType" );
     if ( defaultFS.isEmpty() )
         defaultFS = QStringLiteral( "ext4" );
+    else
+        cDebug() << "Partition-module setting *defaultFileSystemType*" << defaultFS;
     if ( FileSystem::typeForName( defaultFS ) == FileSystem::Unknown )
     {
         cWarning() << "Partition-module setting *defaultFileSystemType* is bad (" << defaultFS << ") using ext4.";

src/modules/partition/partition.conf

@@ -53,6 +53,8 @@ alwaysShowPartitionLabels: true
 #
 # Suggested values: ext2, ext3, ext4, reiser, xfs, jfs, btrfs
 # If nothing is specified, Calamares defaults to "ext4".
+#
+# Names are case-sensitive and defined by KPMCore.
 defaultFileSystemType:  "ext4"
 
 # Show/hide LUKS related functionality in automated partitioning modes.