Merge branch 'jk/config-cleanup'

Code clean-up around use of configuration variables. * jk/config-cleanup: sequencer: simplify away extra git_config_string() call gpg-interface: drop pointless config_error_nonbool() checks push: drop confusing configset/callback redundancy config: use git_config_string() for core.checkRoundTripEncoding diff: give more detailed messages for bogus diff.* config config: use config_error_nonbool() instead of custom messages imap-send: don't use git_die_config() inside callback git_xmerge_config(): prefer error() to die() config: reject bogus values for core.checkstat