Merge branch 'sg/completion-zsh-workaround'

Work around zsh segfaulting when loading git-completion.zsh

* sg/completion-zsh-workaround:
  completion: correct zsh detection when run from git-completion.zsh

contrib/completion/git-completion.bash

@@ -3223,7 +3223,10 @@ __gitk_main ()
 	__git_complete_revlist
 }
-if [[ -n ${ZSH_VERSION-} ]]; then
+if [[ -n ${ZSH_VERSION-} ]] &&
+   # Don't define these functions when sourced from 'git-completion.zsh',
+   # it has its own implementations.
+   [[ -z ${GIT_SOURCING_ZSH_COMPLETION-} ]]; then
 	echo "WARNING: this script is deprecated, please see git-completion.zsh" 1>&2
 	autoload -U +X compinit && compinit

contrib/completion/git-completion.zsh

@@ -39,7 +39,7 @@ if [ -z "$script" ]; then
 		test -f $e && script="$e" && break
 	done
 fi
-ZSH_VERSION='' . "$script"
+GIT_SOURCING_ZSH_COMPLETION=y . "$script"
 __gitcomp ()
 {