--all should report which files it failed to instrument

[novemberborn]

#173 uses --all on a file containing unrecognized syntax. Requiring babel-core/register is the correct solution but it's unfortunate that nyc spits out a rather deep stack trace. Instead it should report which file it failed to instrument, offering suggestions regarding excluding those files or hooking up a transpiler.

[bcoe]

@novemberborn I think the new approach used for --all on the 7.x branch might address this problem, if you get a second take a look.

[tp]

Also had issues with --all, upgrading to [email protected] fixed the issue.