core/include/arch/irq_arch.h: fix typo and trailing whitespaces
Merge pull request #1308 from N8Fear/fix-typo-and-whitespaces

core/include/arch/irq_arch.h: fix typo and trailing whitespaces
core: allow changing the priority at runtime

Closes #198.
pthread: pthread_barrier should call yield
tests: clean up test_pthread_barrier Makefile
tests: add sched_set_priority() test