astyle run [ci skip]
Preprocessor: set error flag when unhandled characters are found so checking can bailout
travis: replace kernel check with clang check.

Check clang instead of kernel, which is a lot faster.
Make clang check failure fatal to the build.
travis: run test_matchcompiler.py
travis: move CHECK_INTERNAL check up, remove "SRCDIR=build VERIFY=1" job in favor of "MAKEFLAGS="HAVE_RULES=yes" SRCDIR=build VERIFY=1"
travis: add -DCHECK_INTERNAL to the VERIFY=1 job to automatically fetch issues like #5869 via travis