boards/mbed_lpc1768: disable DEBUG by default

Set ENABLE_DEBUG from (1) to (0)
native: add and use callback type
Merge pull request #1898 from LudwigOrtmann/native_callback_t

native: add and use callback type
cpu/sam3x8e: fixes to timer driver

- renamed config variable
- placed thread_yield() correctly
cpu/sam3x8e: put PendSV IRQ to lowest prio
cpu/sam3x8e: added output to isr_hard_fault
cpu/sam3x8e: fixed style in startup.c
drivers/mq3: added driver for alcohol sensor
tests: added test for MQ-3 alcohol sensor driver
board/stm32f4discovery: added ADC feature
Merge pull request #1703 from haukepetersen/add_driver_mq3

drivers/mq3: added driver for MQ-3 alcohol sensor
Enable SPI for udoo boards
Merge pull request #1897 from PeterKietzmann/add_udoo_spi

boards/udoo: added peripheral SPI definitions
Merge pull request #1825 from haukepetersen/fix_sam3x_misc

cpu/sam3x8e: general fixes
core: eliminate warning

This initialized has actually no relevance and is just needed to
suppress a compiler warning.
core: update irq_arch documentation
Merge pull request #1901 from OlegHahm/hwtimer_irq_fixup

core: eliminate warning in hwtimer
core: move optional tcb members to DEVELHELP
native: remove obsolete line
sys: Initial import of analytical object dump (od) module