bug#3424: align-regexp: Infinite loop with default regexp

[Teemu Likonen]

The align-regexp command enters infinite loop when it is used with the
default regexp and with REPEAT argument. It's seems to be because the
regexp \s-* matches also zero-length strings.

Steps to reproduce:

 1. Put the following line to the *scratch* buffer:

        foo bar

 2. Put the line inside a region

 3. Type command:

        C-u M-x align-regexp RET \(\s-*\) RET 1 RET 1 RET y

 4. Loop infinitely.


I suggest changing the default regexp to \(\s-+\), like the attached
patch illustrates.

diff --git i/lisp/align.el w/lisp/align.el
index 0917e7d..ea36302 100644
--- i/lisp/align.el
+++ w/lisp/align.el
@@ -933,7 +933,7 @@ region, call `align-regexp' and type in that regular 
expression."
     (list (region-beginning) (region-end))
     (if current-prefix-arg
        (list (read-string "Complex align using regexp: "
-                          "\\(\\s-*\\)")
+                          "\\(\\s-+\\)")
              (string-to-number
               (read-string
                "Parenthesis group to modify (justify if negative): " "1"))
@@ -941,7 +941,7 @@ region, call `align-regexp' and type in that regular 
expression."
               (read-string "Amount of spacing (or column if negative): "
                            (number-to-string align-default-spacing)))
              (y-or-n-p "Repeat throughout line? "))
-      (list (concat "\\(\\s-*\\)"
+      (list (concat "\\(\\s-+\\)"
                    (read-string "Align regexp: "))
            1 align-default-spacing nil))))
   (let ((rule