Merge changes made in Gnus trunk.

Merge changes made in Gnus trunk.

nnmaildir.el (nnmaildir-request-accept-article): Don't call `unix-sync' unless it's defined.
gnus-art.el (gnus-article-stop-animations): Use `elt' instead of `aref' for XEmacs compatibiltiy.
spam.el (spam-fetch-field-fast): Rewrite slightly for clarity.
gnus-sum.el (gnus-summary-refer-thread): Since lambdas aren't closures, quote the form properly (bug#9194).
gnus-sum.el (gnus-summary-insert-new-articles): Clean up slightly.
 (gnus-summary-insert-new-articles): Protect against servers that are down.