Merge branch 'refs/heads/kohana_v3.2/fix/20121218-xls_add_headings' into kohana_v3.2/master
adding a char limit on in XLS::clean_sheet_name()

of 31 characters
Merge branch 'refs/heads/kohana_v3.2/feature/xls_sheet_title_length' into kohana_v3.3/master