mergestate: make clean() only be about creating a clean mergestate
This is similar to the previous patch, but moves the separation one
step further out, to `merge.py`.
Differential Revision: https://phab.mercurial-scm.org/D9034
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: ForIndentation
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
AllowShortBlocksOnASingleLine: false
AllowShortFunctionsOnASingleLine: false
IncludeCategories:
- Regex: '^<'
Priority: 1
- Regex: '^"'
Priority: 2