obslog: redefine default output as a template, unless -f was given
This was easier than I expected to do without affecting any test
output at all.
`hg obslog -f` is pretty broken with templating. For example, it
inserts a single "date" field, but it provides two values for it if
the dates are different. That results in a traceback when running
e.g. `hg obslog -f -Tfoo` with non-local obsmarkers with different
dates. We need to figure out what we want to put in the template for
the filtered case. I've just left it out for now.
{"pattern": "glob:hgext3rd/**/*.py", "tool": "byteify-strings"}