Summary generation still slow

[Uday Reddy]

Summary generation is still needlessly slow. For instance doing delete-label or add-label on an entire folder takes a long time to regenerate the summary.

A trace shows that vm-tokenized-summary-insert calls vm-decode-mime-encoded-words-in-string. It is not clear why this is needed because the summary should be able to use the cached-data fields to get all the information it needs.

See Bug 614570 for background on other reasons for the summary being slow.