fix(tree): work around bash-4.2 bug of [[ ${arr[*]} == *text* ]]

Bash 4.2 has a bug that the following test results in the exit status
1.

$ a=(1 2 ''); [[ ${a[*]} == *\ 2\ * ]]

To work around the problem caused by this behavior, in the `tree'
completion, we store the value of ${words[*]} in a scalar local
variable `line' and use it for the test.

Author: akinomyoga

completions/tree

@@ -30,7 +30,10 @@ _comp_cmd_tree()
         return
     fi
 
-    if [[ ${words[*]} == *\ --fromfile\ * ]]; then
+    # Note: bash-4.2 has a bug with [[ ${arr[*]} == *text* ]], so we
+    # assign ${words[*]} in a temporary variable "line".
+    local line="${words[*]}"
+    if [[ $line == *\ --fromfile\ * ]]; then
         _filedir
     else
         _filedir -d