patch 8.0.0431: 'cinoptions' cannot set indent for extern block

Problem:    'cinoptions' cannot set indent for extern block.
Solution:   Add the "E" flag in 'cinoptions'. (Hirohito Higashi)
diff --git a/runtime/doc/indent.txt b/runtime/doc/indent.txt
index fdb7c67..efb0a7d 100644
--- a/runtime/doc/indent.txt
+++ b/runtime/doc/indent.txt
@@ -325,6 +325,21 @@
 		      void function();       void function();
 		  }                          }
 <
+							*cino-E*
+	EN    Indent inside C++ linkage specifications (extern "C" or
+	      extern "C++") N characters extra compared to a normal block.
+	      (default 0).
+
+		cino=			   cino=E-s >
+		  extern "C" {               extern "C" {
+		      void function();       void function();
+		  }                          }
+
+		  extern "C"                 extern "C"
+		  {                          {
+		      void function();       void function();
+		  }                          }
+<
 							*cino-p*
 	pN    Parameter declarations for K&R-style function declarations will
 	      be indented N characters from the margin.  (default
@@ -554,7 +569,7 @@
 
 
 The defaults, spelled out in full, are:
-	cinoptions=>s,e0,n0,f0,{0,}0,^0,L-1,:s,=s,l0,b0,gs,hs,N0,ps,ts,is,+s,
+	cinoptions=>s,e0,n0,f0,{0,}0,^0,L-1,:s,=s,l0,b0,gs,hs,N0,E0,ps,ts,is,+s,
 			c3,C0,/0,(2s,us,U0,w0,W0,k0,m0,j0,J0,)20,*70,#0
 
 Vim puts a line in column 1 if: