jquery.tablesorter: Reset unaffected columns' sort counts when sorting

jquery.tablesorter: Reset unaffected columns' sort counts when sorting

The column sort count (which is used to determine the sort order when
clicking a table header cell) was not reset on table columns unaffected
by the sorting. Sorting a column in ascending order, then sorting another
column and finally sorting the first column again would cause that column
to be sorted in descending order although it should be ordered in the
default (ascending) order again (see test added).

Change-Id: I3dd49bab07f9a02d9e1d531f1397396025fe77e0