Only load .exe suffix'd completions on Cygwin.

The only platform which actually needs to define .exe suffixes as
part of its completion set is Cygwin.  So don't define them on any
other platform.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

contrib/completion/git-completion.bash

@@ -350,6 +350,7 @@ complete -o default -o nospace -F _git_log git-whatchanged
 # when the user has tab-completed the executable name and consequently
 # included the '.exe' suffix.
 #
+if [ Cygwin = "$(uname -o 2>/dev/null)" ]; then
 complete -o default -o nospace -F _git git.exe
 complete -o default            -F _git_branch git-branch.exe
 complete -o default -o nospace -F _git_cat_file git-cat-file.exe
@@ -361,3 +362,4 @@ complete -o default            -F _git_merge_base git-merge-base.exe
 complete -o default -o nospace -F _git_push git-push.exe
 complete -o default -o nospace -F _git_log git-show-branch.exe
 complete -o default -o nospace -F _git_log git-whatchanged.exe
+fi