Fix map default values and IniIncludeDefaults

These are actually two bugs but it is better to fix them together.
(1) The deepEqual for the ini option IniIncludeDefaults is wrong as it needs to use the actual values of reflect.Value
(2) Fixing (1) reveals that Group.storeDefaults needs to copy maps as otherwise the same map is used for option.value and option.defaultValue

I have also rewritten TestWriteIni to use a table driven test.