Merge branch 'fix-non-ascii-worksheet-names' of git://github.com/maximerety/writeexcel into maximerety-fix-non-ascii-worksheet-names
Merge branch 'master' of github.com:cxn03651/writeexcel
Worksheet#check_sheetname_valid_chars : setting str more simple.
Worksheet#check_sheetname_valid_chars : extract conditional.