Initialize the rtimer component on native platform's startup.

Otherwise applications that use rtimers die when run as native code because of an unhandled signal.
Make native platform's main loop less noisy.
Explicitly initialize queue buffer in the main startup routine only if uIP is used.

The Rime stack already does this on its own, and there is no need to do it twice.
Fix inconsistent usage of short/long integer type in mbxxx platform's configuration file.

The type used to store rtimer ticks on this platform is 32-bit integer, but the macro uses 16-bit comparison.
As a result, the output of the RTIMER_CLOCK_LT(a,b) macro was incorrect when used for comparisons between time values with sufficiently large difference.
The code to repeat this problem on mbxxx platform:

  rtimer_clock_t a = 6 * RTIMER_ARCH_SECOND;
  rtimer_clock_t b = 0;
  printf("%d\n", RTIMER_CLOCK_LT(a,b)); // expected output: "0", actual: "1"
Confine CC2538 WDT on/off conf inside the driver

Instead of requiring all calls to `watchdog_start` to be
wrapped inside `#if WATCHDOG_CONF_ENABLE` guards, we control
things from within the WDT driver itself.

This commit also includes some minor documentation and
indentation cleanups
Fix MODULES for the Sensinode platform
CC2538: Add hardware flow control (RTS/CTS) support on UART1.
Merge pull request #683 from g-oikonomou/sensinode-modules

Fix MODULES for the Sensinode platform
Merge pull request #682 from g-oikonomou/watchdog-cc2538

Confine CC2538 WDT on/off conf inside the driver
Merge pull request #691 from hexluthor/rts-cts

CC2538: Add hardware flow control (RTS/CTS) support on UART1.
Adding tunslip to gitignore
Merge pull request #703 from sieben/gitignore

Adding tunslip to gitignore
Merge pull request #656 from atiselsts/native_platform_patches

Minor improvements for the native platform
Merge pull request #655 from atiselsts/stm32_patches

Fix inconsistent usage of short/long integer type in mbxxx platform's configuration file.