Revert "cpu/cc2538: sbrk() checks if the requested memory is really available."

This reverts commit 81dea364a5b372ad1625181eff710c095420735c.
board/iot-lab_M3: added I2C ISR defines
cpu/stm32f1: fixes to i2c driver

- fixes BUSY on initialization
Merge pull request #1938 from haukepetersen/fix_stm32f1_morei2c

cpu/stm32f1: fixes to i2c driver
malloc: check if the requested memory is really available
resurrect malloc test
lsm303dlhc: initial import of lsm303dlhc driver

TODO: Accelerometer does not return valid values yet
Merge pull request #1782 from benpicco/fix_malloc

check if the requested memory is really available in _sbrk_r
core: [in] parameters should be const in msg.c
Merge pull request #1912 from thomaseichinger/lsm303dlhc

lsm303dlhc: initial import of lsm303dlhc driver
core: always check if the target has a message queue
tests: Add automatic test for msg_send_receive
Merge pull request #1944 from authmillenon/msg_send_receive-test

tests: Add automatic test for msg_send_receive
Merge remote-tracking branch 'origin/master' into X