cat: explicitly document the supported formatter rules...
cat: explicitly document the supported formatter rules
The previous documentation pointed to the export command, but even if the user
recognized that instead of only reading the cat specific list of rules, not all
of the export rules applied anyway (specifically %N, %n and %m). The new items
are a copy/paste from export's list. These rules have existed since at least
version 0.5.
Note that %m gets substituted with 'None' because the commit message isn't
passed to cmdutil.makefilename(). %R and %r are currently effectively the same,
since no revwidth is passed, however they both work.
There aren't any existing tests for these rules, so they are added to prevent
future regression.
