core: Fix/refactor function naming in core/incude/irq.h

boards/arduino-mega2560/board.c

boards/avsextrem/drivers/avsextrem-smb380.c

boards/chronos/board_init.c

boards/msb-430-common/board_init.c

boards/qemu-i386/x86_board_init.c

boards/wsn430-common/board_init.c

core/atomic.c

core/c11_atomic.c

core/include/arch/irq_arch.h

core/include/irq.h

core/include/sched.h

core/kernel_init.c

core/msg.c

core/mutex.c

core/panic.c

core/sched.c

core/thread.c

cpu/arm7_common/VIC.c

cpu/atmega2560/periph/timer.c

cpu/atmega_common/thread_arch.c