Merge branch 'pw/3.0-commentchar-auto-deprecation'

"core.commentChar=auto" that attempts to dynamically pick a suitable comment character is non-workable, as it is too much trouble to support for little benefit, and is marked as deprecated. * pw/3.0-commentchar-auto-deprecation: commit: print advice when core.commentString=auto config: warn on core.commentString=auto breaking-changes: deprecate support for core.commentString=auto