Update minimum Web2py version in update check.

This protects against the issue Somay and Vishrut ran into, having a Web2py before DAL classes acquired as_dict. The specified minimum is a fairly recent version, but (it turns out) there were a string of revisions dealing with DAL as_dict and friends, and the latest was a bug fix at the specified revision.

There was also a change in the format of the Web2py version, that came with a switch in regex in parse_version.  A too-old Web2py will throw an exception -- update check catches this now.

Don't hit me, but I changed the handling of the switch by Web2py to keeping its version in unparsed form -- the check now documents what the change was.