Fix Filesystem.File setReadonly() and isWritable().
Fix Filesystem.File setReadonly() and isWritable().

Use Poco::File for performing file permissions on all platforms.

wyrover/titanium_desktop,appcelerator/titanium_desktop,jvkops/titanium_desktop,wyrover/titanium_desktop,wyrover/titanium_desktop,wyrover/titanium_desktop,appcelerator/titanium_desktop,jvkops/titanium_desktop,appcelerator/titanium_desktop,wyrover/titanium_desktop,jvkops/titanium_desktop,jvkops/titanium_desktop,wyrover/titanium_desktop,appcelerator/titanium_desktop,jvkops/titanium_desktop,appcelerator/titanium_desktop,jvkops/titanium_desktop