Added first c-level ping implementation for linux.
Added lib to manifest, used fixed-length types in C code.

- Fixed bug with #including wrong C file.
Started adding c implementation of ping call.

- Since the popen/pclose combo seemed to not work under regular
  firefox, I've implemented the same in C without popen/pclose.  -
  Added ping_linux.c containing a ping implementation.  - Compile into
  libraries/crossbear_linux_32.so and libraries/crossbear_linux_64.so
  using "gcc -shared -fPIC ping_linux.c -m32 -march=i686 -o  crossbear_linux_32.so" and
  "gcc -shared -fPIC ping_linux.c -mtune=generic -o crossbear_linux_64.so".
Made valgrind happy with ping_linux.
Added is_valid_ip function

There were still usages of malloc and free in CBTracer, so I
implemented a native C is_valid_ip function.
Fixed typos, ignored return value.

No longer freeing the return string when ping returned an error, since
js ignores the ping return value, and uses the return string.
Added some debugging info to requests.
Moved trust cache button to addon menu so we can pass in cbfrontend properly.
Actually using new C functions now in CBTracer.