timestamps: use fully qualified, unambiguous, standard format

[Zooko]

Please use ISO-8601, except with "_" instead of "T" for the separating character for all timestamps. Please include the ISO-8601 unambiguous timezone indicator (which is either "Z" or a number of hours offset from UTC).

Here is Markus Kuhn's advocacy and summary of ISO-8601:

• ​http://www.cl.cam.ac.uk/~mgk25/iso-time.html

Here is the related discussion from the Tahoe trac:

• ​http://allmydata.org/trac/tahoe/ticket/326 # use consistent time stamps in logging

Here are some Python implementations of ISO and/or UTC timestamps:

• ​http://allmydata.org/trac/tahoe/browser/src/allmydata/node.py?rev=2731#L30
• ​http://allmydata.org/trac/tahoe/browser/src/allmydata/util/time_format.py?rev=2424#L12
• ​http://allmydata.org/trac/pyutil/browser/pyutil/pyutil/time_format.py?rev=93

This ticket is the more urgent, less controversial subset of #90 (timestamps: formatting and timezones).

[Brian Warner]

reformatted summary a bit