Insert keys at the start of the typeahead buffer

When sending keys to Vim, they are by default added to the end of the typeahead
buffer. If there are already keys in the buffer, they will be processed first
and may change the state that our keys combination was sent for (e.g.
<C-X><C-U><C-P> in normal mode instead of insert mode or <C-e> outside of
completion mode). We avoid that by inserting the keys at the start of the
typeahead buffer.

autoload/youcompleteme.vim

@@ -533,10 +533,22 @@ function! s:PollFileParseResponse( ... )
 endfunction
 
 
+function! s:SendKeys( keys )
+  " By default keys are added to the end of the typeahead buffer. If there are
+  " already keys in the buffer, they will be processed first and may change the
+  " state that our keys combination was sent for (e.g. <C-X><C-U><C-P> in normal
+  " mode instead of insert mode or <C-e> outside of completion mode). We avoid
+  " that by inserting the keys at the start of the typeahead buffer with the 'i'
+  " option. Also, we don't want the keys to be remapped to something else so we
+  " add the 'n' option.
+  call feedkeys( a:keys, 'in' )
+endfunction
+
+
 function! s:OnInsertChar()
   call timer_stop( s:pollers.completion.id )
   if pumvisible()
-    call feedkeys( "\<C-e>", 'n' )
+    call s:SendKeys( "\<C-e>" )
   endif
 endfunction
 
@@ -745,7 +757,7 @@ function! s:Complete()
   " automatically replaces the current text with it. Calling <c-p> forces Vim to
   " deselect the first candidate and in turn preserve the user's current text
   " until he explicitly chooses to replace it with a completion.
-  call feedkeys( "\<C-X>\<C-U>\<C-P>", 'n' )
+  call s:SendKeys( "\<C-X>\<C-U>\<C-P>" )
 endfunction