Logging system and throwing of exceptions instead of quitting.

[dtmoodie]

Hi,

Currently caffe quit's whenever a glog check fails. This is undesirable when integrating into C++ applications, because now my whole program can quit for no apparent reason (to the user) when given bad input. Furthermore it can be bad when I've already done a lot of processing in ipython, only to find a spelling error crashes my whole session.
This may just be due to how glog works on window's, but I was under the impression that it's similar on Linux. I propose a shift to throwing exceptions instead.

Furthermore, since boost is already a requirement, why not use boost logging instead of glog?
It shouldn't be terribly difficult to write a set of equivalent macros using boost logging to throw an exception instead.

[lukeyeager]

For context, check out #1683.

[shelhamer]

I hear the grievances against crashing, but switching to exceptions would require a lot of care and many of the errors can't be recovered from. That said, my stance has been that of #1683 (comment). I'm closing this to keep the conversation at #1683.