review fixes

doc/UltiSnips.txt

@@ -1443,11 +1443,15 @@ Specified code will be evaluated at stages defined above and same global
 variables and modules will be available that are stated in
 the *UltiSnips-context-snippets* section.
 
+                                                *UltiSnips-buffer-proxy*
+
 Note: special variable called 'snip.buffer' should be used for all buffer
 modifications. Not 'vim.current.buffer' and not 'vim.command("...")', because
 of in that case UltiSnips will not be able to track changes buffer from
 actions.
 
+'snip.buffer' has the same interface as 'vim.current.window.buffer'.
+
 4.10.1 Pre-expand actions                       *UltiSnips-pre-expand-actions*
 
 Pre-expand actions can be used to match snippet in one location and then

pythonx/UltiSnips/buffer_proxy.py

@@ -85,7 +85,8 @@ class VimBufferProxy(_vim.VimBuffer):
             raise RuntimeError('buffer was modified using vim.command or ' +
             'vim.current.buffer; that changes are untrackable and leads to ' +
             'errors in snippet expansion; use special variable `snip.buffer` '
-            'for buffer modifications')
+            'for buffer modifications.\n\n' +
+            'See :help UltiSnips-buffer-proxy for more info.')
 
     def __setitem__(self, key, value):
         """

test/vim_test_case.py

@@ -128,7 +128,6 @@ class VimTestCase(unittest.TestCase, TempFileManager):
         vim_config.append('set fileencoding=utf-8')
         vim_config.append('set buftype=nofile')
         vim_config.append('set shortmess=at')
-        vim_config.append('set cmdheight=10')
         vim_config.append('let @" = ""')
         assert EX == "\t"  # Otherwise you need to change the next line
         vim_config.append('let g:UltiSnipsExpandTrigger="<tab>"')