ARM: Be aware of ARMEL and ARMEL

* My BeagleBone gcc defines __ARMEL__ but not
  __ARM__ which breaks the native tool builds
* As ARM was originally Little Endian, we assume
  __ARM__ means as such.
* Look for Big Endian ARM and define the needed big
  endian preprocessors
HttpRequest: close the connection on Stop()

When calling Stop(), we expect the request thread to exit as soon as
possible. Closing the connection unlocks it from any blocking read() or
write(), avoiding some lockup situations.