logging: format strings are goofy

[Brian Warner]

I should have just followed Twisted's lead w.r.t. flogging format strings. The goal is to allow at least these two forms:

• log.msg("blah")
• log.msg("blah %s", posarg)

(twisted doesn't offer the second, but I think it's handy).

The other goal is to allow kwarg formatting. Twisted does log.msg(format="blah %(n)d", n=12), but I went with log.msg("blah %(n)d", n=12). The problem with my approach is that it means you can't tell if the user really wanted string formatting or not, so log.msg("100% done!") causes a ValueError? or something as the percent-space format key is bogus.

Switch to the Twisted approach. Then, only apply formatting if there are positional args, or if we have format= instead of message=. Note that this means not all events will have message=, so other code must be prepared to handle this.

[Brian Warner]

This is fixed, in [f21098749f883582f58830c1192b80702483fb96].