Restore bash completion behaviour for bash 4.x

In Pull Request #178, the use of `builtin compopt` as a test condition
is inappropriate.  Use `[[ $(type -t compopt) = "builtin" ]]` instead.

Also clean up formatting of the resulting bash completion script.

bash_completions.go

@@ -60,7 +60,7 @@ __handle_reply()
     __debug "${FUNCNAME}"
     case $cur in
         -*)
-            if builtin compopt > /dev/null 2>&1; then
+            if [[ $(type -t compopt) = "builtin" ]]; then
                 compopt -o nospace
             fi
             local allflags
@@ -70,7 +70,7 @@ __handle_reply()
                 allflags=("${flags[*]} ${two_word_flags[*]}")
             fi
             COMPREPLY=( $(compgen -W "${allflags[*]}" -- "$cur") )
-            if builtin compopt > /dev/null 2>&1; then
+            if [[ $(type -t compopt) = "builtin" ]]; then
                 [[ $COMPREPLY == *= ]] || compopt +o nospace
             fi
             return 0;
@@ -220,13 +220,13 @@ func postscript(out *bytes.Buffer, name string) {
 }
 
 `, name)
-	fmt.Fprintf(out, `
-		if builtin compopt > /dev/null 2>&1; then
+	fmt.Fprintf(out, `if [[ $(type -t compopt) = "builtin" ]]; then
     complete -F __start_%s %s
-		else
+else
     complete -o nospace -F __start_%s %s
-		fi
-		`, name, name, name, name)
+fi
+
+`, name, name, name, name)
 	fmt.Fprintf(out, "# ex: ts=4 sw=4 et filetype=sh\n")
 }