Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

nnir.el: General clean-up, and reimplementation of various bits.
nnir.el (nnir-search-engine): Ressurect variable, since it's used later in the file.
shr.el (shr-generic): The text nodes should be text, not :text.
nnir.el: Move defvars around to silence compiler warnings.
shr.el (shr-tag-img): Output "*" instead of "[img]".