test/test_26_autofilter.rb:   'x = Blanks"  pass.   other not.
test/test_26_autofilter.rb:
  'x = Blanks"  pass.   other not.

lib/spreadsheet/worksheet.rb:
  bug fix.

cxn03651/writeexcel,cxn03651/writeexcel,Orphist/writeexcel,Orphist/writeexcel