Merge branch 'ab/help-fixes'

Merge branch 'ab/help-fixes'

Updates to how command line options to "git help" are handled.

* ab/help-fixes:
  help: don't print "\n" before single-section output
  help: add --no-[external-commands|aliases] for use with --all
  help: error if [-a|-g|-c] and [-i|-m|-w] are combined
  help: correct usage & behavior of "git help --all"
  help: note the option name on option incompatibility
  help.c: split up list_all_cmds_help() function
  help tests: test "git" and "git help [-a|-g] spacing
  help.c: use puts() instead of printf{,_ln}() for consistency
  help doc: add missing "]" to "[-a|--all]"