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
Merge pull request #1912 from thomaseichinger/lsm303dlhc

lsm303dlhc: initial import of lsm303dlhc driver
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
board/iot-lab_M3: configured GPIOs correctly
Merge pull request #1946 from haukepetersen/fix_iotlab_lsmdriverdefines

board/iot-lab_M3: configured GPIOs correctly
iot-lab_M3: set baud rate to 500 kbaud

The IoT-Lab testbed requires a baud rate of 500 kbaud to use UART.
Hence, this commit sets the default baud rate to this value and adapt
the `make term` target accordingly.
iot-lab_M3: don't overwrite a custom baud rate
iot-lab_M3: complement stdio documentation