Changes test

As a simple RCS sort of thing, changes are now kept in a single file.

I'm using "<<<" as the delimiter, and saving user, path, and time metadata.

The time is in unixtime format, in UTC.

Trying to keep the PUT handler quite small. It's 84 lines at the moment.

Comments by dpk

What happens if someone does PUT with a line starting with "<<<"? Perhaps do something like mboxrd / SMTP '.' for this. But that's ughy, imho: I'd tend to prefer a length-prefixed format. But it would have be a count of lines, not bytes, to avoid mboxcl-style portability problems.

A summary file would make this format much more efficient.