font-lock \ #foo in shell mode more correctly

* lisp/progmodes/sh-script.el (sh-syntax-propertize-function):
\ #foo isn't a comment -- it's a symbol that starts with a space
character (bug#17538).

lisp/progmodes/sh-script.el

@@ -1141,7 +1141,7 @@ subshells can nest."
     ;; metacharacters.  The list of special chars is taken from
     ;; the single-unix spec of the shell command language (under
     ;; `quoting') but with `$' removed.
-    ("\\(?:[^|&;<>(`\\\"' \t\n]\\|\\${\\)\\(#+\\)" (1 "_"))
+    ("\\(?:[^|&;<>(`\\\"' \t\n]\\|\\${\\|\\ \\)\\(#+\\)" (1 "_"))
     ;; In addition, `#' at the beginning of closed parentheses
     ;; does not start a comment if the parentheses are not isolated
     ;; by metacharacters, excluding [()].