fixed another SQLFORM.formstyles, thanks Anthony

gluon/sqlhtml.py

@@ -1079,7 +1079,7 @@ class SQLFORM(FORM):
 
     def createform(self, xfields):
         if isinstance(self.formstyle, basestring):
-            if self.formstyle in self.formstyles:
+            if self.formstyle in SQLFORM.formstyles:
                 self.formstyle = SQLFORM.formstyles[self.formstyle]
             else:
                 raise RuntimeError, 'formstyle not found'