Add stub setjmp/longjmp implementation for support libpng/libjpeg.
Add more softfloat used by libjpeg.
Enable usb debugging by default (sysctls or tunables are required to actually
trigger output.)

Add mouse support.
The malloc from rtld is broken under the sandbox ABI (probably due
to doing unallowable things with pointers) so replace it with our old
non-freeing malloc.  This version has grown support for realloc.
In sandbox mode avoid possiably reading past the end of the capability
by accident by doing a simple byte by byte comparsion.  A smarter
version that checks the lenght of the capability and uses capability
registers should be possible.
Temprorarily add a copy of cheri_helloworld-helper that doesn't use any
libraries to aid David in hunting printf issues.  I've not hooked it to
the build as it should be removed soon.