patch 8.0.0559: setting ttytype to xxx does not always fail

Problem:    Setting ttytype to xxx does not always fail as expected. (Marvin
            Schmidt)
Solution:   Catch both possible errors. (closes #1601)

src/testdir/test_options.vim

@@ -280,10 +280,22 @@ func Test_set_ttytype()
     set ttytype=xterm
     call assert_equal('xterm', &ttytype)
     call assert_equal(&ttytype, &term)
-    " FIXME: "set ttytype=" gives E522 instead of E529
-    " in travis on some builds. Why? Commented out this test for now.
-    " call assert_fails('set ttytype=', 'E529:')
-    call assert_fails('set ttytype=xxx', 'E522:')
+    " "set ttytype=" gives E522 instead of E529
+    " in travis on some builds. Why?  Catch both for now
+    try
+      set ttytype=
+      call assert_report('set ttype= did not fail')
+    catch /E529\|E522/
+    endtry
+
+    " Some systems accept any terminal name and return dumb settings,
+    " check for failure of finding the entry and for missing 'cm' entry.
+    try
+      set ttytype=xxx
+      call assert_report('set ttype=xxx did not fail')
+    catch /E522\|E437/
+    endtry
+
     set ttytype&
     call assert_equal(&ttytype, &term)
   endif

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    559,
 /**/
     558,
 /**/