Fix display of modified/accessed dates in local time zone.

Partially reverts 5227bd311291a7846d352938559e27525acb4cdf.  That commit changed the code to convert the libssh2 UTC times into the local time zone.  However, it appears that Explorer expects the OLE DATE (VT_DATE) variant to be in UTC format, so the timezone conversion is happening twice.  Explorer's expectation isn't documented anywhere that we could find.  The following docs for PropVariantToFileTime is the closest we could find: http://goo.gl/Z56FKb.

It's not clear why we thought commit 5227bd3 fixed #121 and #139 or why those bugs occurred at all.  Perhaps a problem elsewhere, that has since been fixed, caused those problems and 5227bd3 masked it despite being the wrong fix.  Hopefull this change won't reintroduce those bugs.

Relates #121.
Relates #139.
Fixes #231.
Merge branch 'feauture/fix_time_zone' into develop