cpu/nrf51822: changed ISR stack size to 512 byte
boards: adjusted TIMER_0 defines for NRF based b.

adjusted for
- pca10000
- pca10005
- yunjia-nrf51822
cpu/nrf51822: fixed timers

- changed TIMER_0 to be a 24-bit timer -> see Nordic PAN #32
- cleaned up timer initialization code
- added check if an interrupt channel was active
cpu: adjusted IRQ stack sizes for Cortex CPUs
core: sched.c did not compile with DEBUG=1
boards/cc2538dk: allow the application's makefile to override the UPDATE_CCA parameter, for example:
CFLAGS += -DUPDATE_CCA=0
embunit: fix macros
avr: define ssize_t
Remove special case for atmega in kernel_types.h
board/arduino-due: removed newlines in periph_conf
Merge pull request #1990 from Kijewski/avr-ssize_t

avr: define ssize_t
cpu/sam3x8e: added interrupt mode to uart driver
board/arduino-due: added missing UART defines

- added port defines to periph_conf.h
- added feature to Makefile.features
Merge pull request #1991 from haukepetersen/fix_artuinodue_periphconf

board/arduino-due: removed newlines in periph_conf
board/udoo: added missing UART defines

- added defines to periph_conf.h
- added UART feature to Makefile.features
cpu/sam3x8e: made UART0 work by editing syscalls
Merge pull request #1971 from Kijewski/assert-macros

embunit: fix macros
Merge pull request #1482 from haukepetersen/fix_sam3x_finished_uart

cpu/sam3x: completed low-level UART driver
Merge pull request #1981 from locicontrols/update-cca

boards/cc2538dk: allow the application's makefile to override UPDATE_CCA
iot-lab_M3: flashing works fine w/o device_desc