[$] Process tagging with ptags

For various reasons related to accounting and security, there is recurringinterest in having the kernel identify the container that holds any givenprocess. Attempts to implement that functionality tend to run into thesame roadblock, though: the kernel has no concept of what a "container" is,and there is seemingly little desire to change that state of affairs. A solution to this problem may exist in the form of a neglectedpatch called "ptags", which enables the attachment of arbitrary tags toprocesses.