spam 5.x-3.0-alpha6

This is a bug fix release. It fixes the following bugs:

• bug #274209: support php4, implement form_alter outside of standard adapi
• bug #284336: only display spam links if filtering content type
• bug #284389: validate that tokens exist before using them
• bug #273398: file never got checked in, thus bayesian schema not created
• bug #275614: be sure that we don't divide by zero
• bug #275315: add missing {}'s
• bug #262618: called spam_install() when meant to call spam_upgrade_0()
• added index, addressing a query showing up in my slow query logs