fix error occurs when call sort.clear

when using singleSort and hiddenColumn together, sort a column first,
then hide this very column, and then call sort.clear, an error will
occur.
fix issue in filterPane DateTimeBox

When filter field is a Date type, set condition to isEmpty, the value
should always be empty. But cloase & reopen the filterdialog, the value
will be changed to '1/1/1970'.
That is becasuse in DateTimeBox, setValue('') will set the date to
'1/1/1970'.
Should use setValue(null) instead.
Fix hiddenColumns.add duplicated arguments
Fix edit.begin causing header and body mismatch
A better way to persist column order
fix test_grid_hiddenColumns.html fail
fix selectAll checkbox won't change

selectAll checkbox won't change when setPageSize
fix selectAll issue in IndirectSelectColumn

selectAll checkbox won't change
fix alwaysediting test page error in dojo-1.9

In Dojo-1.9, click the select widget on column select, an error will
occur. That is becaue labelAttr property is not compatible with old
store in Dojo 1.9
fix selectAll issue in IndirectSelect
fix error occur when store and column are empty
fix dod label and input not align in form
fix vLayout won't reLayout when header change

header's refresh will sometimes alter the height of the header, so need
to call vLayout.reLayout()
make rowHoverEffect settable after grid created
fix Locked rows not aligned with RowHeader
Fix exporter initialize arguments
Stop using dojo.create in dod test page
Mouse over can change header height, so need reLayout
Fix adding empty row when using alwaysEditing
Fix grid width when resizing column in autoWidth grid