[1.1.X] Fixed #6510 -- Refactored the way child nodes are found in template...

[1.1.X] Fixed #6510 -- Refactored the way child nodes are found in template nodes to avoid potential inconsistencies. Thanks to SmileyChris for the patch.

Backport of r12654 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12655 bcc190cf-cafb-0310-a4f2-bffc1f526a37