Update to Mongoose 3.9 at the last point before the MIT -> GPL license change

[That is, https://github.com/cesanta/mongoose/commit/04fc209644b414d915c446bb1815b55e9fe63acc. See https://groups.google.com/forum/#!topic/mongoose-users/aafbOnHonkI]

The RTEMS patches described in the following emails and made to the previous Mongoose base have been applied:
  - http://www.rtems.org/pipermail/rtems-devel/2012-July/001345.html
  - http://www.rtems.org/pipermail/rtems-devel/2012-July/001343.html
  - http://www.rtems.org/pipermail/rtems-devel/2012-July/001346.html (except to mongoose.1, see below)
...as well as a patch very similar to that discussed at http://forums.bannister.org/ubbthreads.php?ubb=showflat&topic=7600&gonew=1 to provide poll() (which might be able to go away soon, with incoming RTEMS poll() support)

mg_connect(), mg_url_encode() and mg_vprintf() were additionally marked "static" to silence warnings.

mongoose.1 appears to have been removed from the upstream distribution.

Note that the API's changed, for example:
  - A struct mg_callbacks must now be provided to mg_start(). Initialise members to NULL to disable various types of callbacks
  - Callback interfaces have changed significantly in general
  - The short form of options (e.g., "u" instead of "run_as_user") are no longer available (upstream)
  - The "max_request_size" options has been removed