[1.0.X] Fixed #11278 -- Clarified query documentation regarding bulk...

[1.0.X] Fixed #11278 -- Clarified query documentation regarding bulk assignment of m2m values. Thanks to zgoda for the patch.

Merge of r11045 and r11054 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@11057 bcc190cf-cafb-0310-a4f2-bffc1f526a37