Various Updates for 8051-based Platforms

This is a series of updates for the Sensinode and CC2530DK platforms

Importantly:
* Both platform build systems now support verbosity control. This comes with a change which disables two specific SDCC warnings (110 and 126). Both those warnings relate to various code optimisations (e.g. dead code elimination) and increase build verbosity without adding any real knowledge.
* Decreased code size for some Sensinode examples. @nvt, @adamdunkels : #307 should pass all Sensinode regression tests with this in place.
* The CC2531 USB Dongle now identifies itself more clearly (as a 'Texas Instruments CC2531 USB Dongle') and uses a TI-provided VID:PID.
* Switching between CC2530 and CC2531 was previously done via a make variable, but the build system doesn't really need to know. Thus, we change things so that we can switch between the two models via a CPP define instead and take advantage of dependency generation.

In other news:
* This Pull Request fixes #286 (thanks, @maheshsutariya).
* Various minor cleanups of both build systems and platform-specific examples