patch 8.1.1526: no numerical value for the patchlevel

Problem:    No numerical value for the patchlevel.
Solution:   Add v:versionlong.
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 5f81560..da45de8 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2173,6 +2173,17 @@
 		version 5.0 and 5.1 may have a patch 123, but these are
 		completely different.
 
+					*v:versionlong* *versionlong-variable*
+v:versionlong	Like v:version, but also including the patchlevel.  Version
+		8.1 with patch 1234 has value 8011234.  This can be used like
+		this: >
+			if v:versionlong >= 8011234
+<		However, if there are gaps in the list of patches included
+		this will not work well.  This can happen if a recent patch
+		was included into an older version, e.g. for a security fix.
+		Use the has() function to make sure the patch is actually
+		included.
+
 				*v:vim_did_enter* *vim_did_enter-variable*
 v:vim_did_enter	Zero until most of startup is done.  It is set to one just
 		before |VimEnter| autocommands are triggered.