[MERGE] (0.17) reworked LogFormatter API

[Aaron Bentley]

Aaron Bentley has voted +1.
Status is now: Semi-approved
Comment:
This looks nice.  Some further tweaks would be:
1. Instead of commenting-out LogFormatter.log_revision, add a 
NewLogFormatter  (or something) class that ShortLogFormatter et al are 
derived from.
2. Move the handling of legacy formatters into a method which takes a 
LogRevision as an parameter.

But I think this is mergeable as is.

Aaron

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C4641DADE.7020806%40gmail.com%3E