Add ycmd-with-handled-server-exceptions macro

[ptrv]

I have this branch for a couple of months and was using it at work without problems.

This PR introduces a new macro ycmd-with-handled-server-exceptions which wraps all boiler-plate code for handling exceptions and running code on exception or if we should bind the current-buffer for the request and response when we need to make sure we run the response code in the buffer that was used for the request.

@abingham What do you think?

[abingham]

The travis build is failing because of a request.el dependency on emacs 24.4. I think this is nonsense, and you change looks like it works fine, so I'll merge it in.

[ptrv]

The problem is the dependencies are not installed with the right Emacs Version. I have the impression that the system emacs is used and not the one we specify. Maybe it's a problem with our makefile. Unfortunately I have not much time to look into this right now

[abingham]

The request.el in their github repo actually specifies emacs-24.4. I've asked for clarification from the project.

[ptrv]

That's fine. The removed some patches for emacs version lower than 24.4. The problem is with installing dependencies on Travis. If you look a the logs, package.el tries to install dependencies into a folder containing 24.3 in the path which indicates that the emacs version is 24.3. I think Cask is not picking up the right version on Travis