Added custom SQL for creating index on tree_path for MySQL
Added custom SQL for creating index on tree_path for MySQL

Almad/django-threadedcomments,PolicyStat/django-threadedcomments,ccnmtl/django-threadedcomments,SmithsonianEnterprises/django-threadedcomments,incuna/django-threadedcomments,SmithsonianEnterprises/django-threadedcomments,coxmediagroup/django-threadedcomments,HonzaKral/django-threadedcomments,coxmediagroup/django-threadedcomments,yrcjaya/django-threadedcomments,nikolas/django-threadedcomments,nikolas/django-threadedcomments,yrcjaya/django-threadedcomments,ccnmtl/django-threadedcomments,HonzaKral/django-threadedcomments