LPC11U35 support for USBDevice and mbed-rtos

I've added support for the EA LPC11U35 QuickStart Board to USBDevice and mbed-rtos. I also fixed several string-related bugs in USBDevice. This pull request is identical to the following two pull requests on the mbed site:

* https://mbed.org/users/mbed_official/code/mbed-rtos/pull-request/2
* https://mbed.org/users/mbed_official/code/USBDevice/pull-request/3

...and is in response to my [conversation with Erik Olieman](http://mbed.org/forum/bugs-suggestions/post/23285/).