Adding a few more problematic C++ .h files to samples.

Adding a few more C++ examples here. In particular ones that have been reported as problematic here: https://github.com/github/linguist/issues/651 .

From what I can tell running specs locally and checking repos that have shown erroneous stats in the past, these latest additions to the training set combined with [this commit](https://github.com/github/linguist/commit/4adbbc3fcc0d2405b706bc1832d4b35114c5843c) by @rhunter means linguist is correctly disambiguating C++ from Objective-C in the vast majority of cases.

Time to cut a new Gem to see if I'm right?