py3: fix formatting of branchmap log messages with repo.filtername=None
`"%s" % None` does not work on py3. I've extracted a little function
for producing a formatted message given the filter name.
Differential Revision: https://phab.mercurial-scm.org/D6644
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2