GPG trustdb batch updates

A while ago, I mused on how network latency affects my email usage - one other cause of slowness in my mail client has been GPG key verification. Occasionally, when Evolution wants to check a signature, gpg takes 30 seconds or more to run, and the text of the message is not displayed until the end. The reason gpg runs so slowly is that it sometimes checks its trust database to make sure it's up to date....