patch 8.1.1307: cannot reconnect to the X server after it restarted

Problem:    Cannot reconnect to the X server after it restarted.
Solution:   Add the :xrestore command. (Adrian Kocis, closes #844)
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index 37577f7..5ec69be 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -1739,6 +1739,9 @@
 EX(CMD_xnoremenu,	"xnoremenu",	ex_menu,
 			RANGE|ZEROR|EXTRA|TRLBAR|NOTRLCOM|USECTRLV|CMDWIN,
 			ADDR_OTHER),
+EX(CMD_xrestore,	"xrestore",	ex_xrestore,
+			EXTRA|TRLBAR|CMDWIN,
+			ADDR_NONE),
 EX(CMD_xunmap,		"xunmap",	ex_unmap,
 			EXTRA|TRLBAR|NOTRLCOM|USECTRLV|CMDWIN,
 			ADDR_NONE),