patch 8.1.1346: error for Python exception does not show useful info

Problem:    Error for Python exception does not show useful info.
Solution:   Show the last line instead of the first one. (Ben Jackson,
            closes #4381)

src/testdir/test_pyx2.vim

@@ -72,3 +72,11 @@ func Test_pyxfile()
     call assert_match(s:py3pattern, split(var)[0])
   endif
 endfunc
+
+func Test_Catch_Exception_Message()
+  try
+    pyx raise RuntimeError( 'TEST' )
+  catch /.*/
+    call assert_match( '^Vim(.*):RuntimeError: TEST$', v:exception )
+  endtry
+endfunc