patch 7.4.1017

Problem:    When there is a backslash in an option ":set -=" doesn't work.
Solution:   Handle a backslash better. (Jacob Niehus)  Add a new test, merge
            in old test.

src/testdir/test_set.vim

@@ -0,0 +1,27 @@
+" Tests for the :set command
+
+function Test_set_backslash()
+  let isk_save = &isk
+
+  set isk=a,b,c
+  set isk+=d
+  call assert_equal('a,b,c,d', &isk)
+  set isk+=\\,e
+  call assert_equal('a,b,c,d,\,e', &isk)
+  set isk-=e
+  call assert_equal('a,b,c,d,\', &isk)
+  set isk-=\\
+  call assert_equal('a,b,c,d', &isk)
+
+  let &isk = isk_save
+endfunction
+
+function Test_set_add()
+  let wig_save = &wig
+
+  set wildignore=*.png,
+  set wildignore+=*.jpg
+  call assert_equal('*.png,*.jpg', &wig)
+
+  let &wig = wig_save
+endfunction