Don't bother defining __get_cwordX on non-applicable bash versions.

bash_completion

@@ -270,6 +270,7 @@ _get_cword()
 # _get_cword, main routine
 # __get_cword4, bash-4 variant
 #
+[ -z "$bash4" ] &&
 __get_cword3()
 {
     if [[ "${#COMP_WORDS[COMP_CWORD]}" -eq 0 ]] || [[ "$COMP_POINT" == "${#COMP_LINE}" ]]; then
@@ -332,6 +333,7 @@ __get_cword3()
 # _get_cword, main routine
 # __get_cword3, bash-3 variant
 #
+[ -n "$bash4" ] &&
 __get_cword4()
 {
     local i