Vim still loves to block the main GUI thread on occasion when asking for
completions... to counteract this stupidity, we enforce a hard budget of 0.5s
for all completion requests. If the server doesn't respond by then (it should,
unless something really bad happened), we give up.
The problem was that when you start vim like "vim foo.cc", the FileReadyToParse
event is sent to the server before it's actually started up. Basically, a race
condition.
We _really_ don't want to miss that event. For C++ files, it tells the server to
start compiling the file.
So now PostDataToHandlerAsync in BaseRequest will retry the request 3 times
(with exponential backoff) before failing, thus giving the server time to boot.
