Merge branch 'sh/mergetool-hideresolved'

"git mergetool" feeds three versions (base, local and remote) of a conflicted path unmodified. The command learned to optionally prepare these files with unconflicted parts already resolved. * sh/mergetool-hideresolved: mergetool: add per-tool support and overrides for the hideResolved flag mergetool: break setup_tool out into separate initialization function mergetool: add hideResolved configuration