patch 8.1.0754: preferred column is lost when setting 'cursorcolumn'

Problem:    Preferred column is lost when setting 'cursorcolumn'.
Solution:   Change option flag to P_RWINONLY. (Takayuki Kurosawa,
            closes #3806)
diff --git a/src/testdir/test_cursor_func.vim b/src/testdir/test_cursor_func.vim
index d784e36..a41cc7d 100644
--- a/src/testdir/test_cursor_func.vim
+++ b/src/testdir/test_cursor_func.vim
@@ -46,3 +46,23 @@
   quit!
 endfunc
 
+" Tests for behavior of curswant with cursorcolumn/line
+func Test_curswant_with_cursorcolumn()
+  new
+  call setline(1, ['01234567', ''])
+  exe "normal! ggf6j"
+  call assert_equal(6, winsaveview().curswant)
+  set cursorcolumn
+  call assert_equal(6, winsaveview().curswant)
+  quit!
+endfunc
+
+func Test_curswant_with_cursorline()
+  new
+  call setline(1, ['01234567', ''])
+  exe "normal! ggf6j"
+  call assert_equal(6, winsaveview().curswant)
+  set cursorline
+  call assert_equal(6, winsaveview().curswant)
+  quit!
+endfunc