[MERGE] [FIX] hr_timesheet_sheet: make it timezone tolerant and avoid errors when...

[MERGE] [FIX] hr_timesheet_sheet: make it timezone tolerant and avoid errors when comparing datetime and dates, courtesy of Yannick Vaucher (Camptocamp)

The attendance date recieved by the server is in UTC while the user sees it in his timezone. This means that an attendance could be in a timesheet (bounded by dates) for a user but not for the server which would not accept a valid attendance.
The fix will make the check in the user's timezone.

Only the date part of the attendance is kept for comparison as the boundaries are dates objects.

bzr revid: mat@openerp.com-20140428153216-4s6r5hu1ov0p0ofm