patch 8.1.1334: when buffer is hidden "F" in 'shortmess' is not used

Problem:    When buffer is hidden "F" in 'shortmess' is not used.
Solution:   Check the "F" flag in 'shortmess' when the buffer is already
            loaded. (Jason Franklin)  Add test_getvalue() to be able to test
            this.
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index eb7a821..e43f57b 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2701,6 +2701,7 @@
 test_autochdir()		none	enable 'autochdir' during startup
 test_feedinput({string})	none	add key sequence to input buffer
 test_garbagecollect_now()	none	free memory right now for testing
+test_getvalue({string})		any	get value of an internal variable
 test_ignore_error({expr})	none	ignore a specific error
 test_null_blob()		Blob	null value for testing
 test_null_channel()		Channel	null value for testing
@@ -9894,6 +9895,11 @@
 		internally, and |v:testing| must have been set before calling
 		any function.
 
+test_getvalue({name})					*test_getvalue()*
+		Get the value of an internal variable.  These values for
+		{name} are supported:
+			need_fileinfo
+
 test_ignore_error({expr})			 *test_ignore_error()*
 		Ignore any error containing {expr}.  A normal message is given
 		instead.