patch 8.0.0463: side effects from resetting 'compatible' in defaults.vim

Problem:    Resetting 'compatible' in defaults.vim has unexpected side
            effects. (David Fishburn)
Solution:   Only reset 'compatible' if it was set.
diff --git a/runtime/defaults.vim b/runtime/defaults.vim
index 43ff1e0..69668f1 100644
--- a/runtime/defaults.vim
+++ b/runtime/defaults.vim
@@ -1,7 +1,7 @@
 " The default vimrc file.
 "
 " Maintainer:	Bram Moolenaar <Bram@vim.org>
-" Last change:	2016 Sep 02
+" Last change:	2017 Mar 08
 "
 " This is loaded if no vimrc file was found.
 " Except when Vim is run with "-u NONE" or "-C".
@@ -21,7 +21,10 @@
 
 " Use Vim settings, rather than Vi settings (much better!).
 " This must be first, because it changes other options as a side effect.
-set nocompatible
+" Avoid side effects when it was already reset.
+if &compatible
+  set nocompatible
+endif
 
 " Allow backspacing over everything in insert mode.
 set backspace=indent,eol,start
diff --git a/src/version.c b/src/version.c
index ff1c9b8..c1ac29d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    463,
+/**/
     462,
 /**/
     461,