Infrastructure for modularizing protocol analyzers.

There's now a new directory "src/protocols/", and the plan is for each
protocol analyzer to eventually have its own subdirectory in there
that contains everything it defines (C++/pac/bif). The infrastructure
to make that happen is in place, and two analyzers have been
converted to the new model, HTTP and SSL; there's no further
HTTP/SSL-specific code anywhere else in the core anymore (I believe :-)

Further changes:

    - -N lists available plugins, -NN lists more details on what these
      plugins provide (analyzers, bif elements). (The latter does not
      work for analyzers that haven't been converted yet).

    - *.bif.bro files now go into scripts/base/bif/; and
      scripts/base/bif/plugins/ for bif files provided by plugins.

    - I've factored out the bifcl/binpac CMake magic from
      src/CMakeLists.txt to cmake/{BifCl,Binpac}

    - There's a new cmake/BroPlugin that contains magic to allow
      plugins to have a simple CMakeLists.txt. The hope is that
      eventually the same CMakeLists.txt can be used for compiling a
      plugin either statically or dynamically.

    - bifcl has a new option -c that changes the code it generates so
      that it can be used with a plugin.

TODOs:
    - "make install" is probably broken.
    - Broxygen is probably broken for plugin-defined events.
    - event groups are broken (do we want to keep them?)

bro-path-dev.in

@@ -12,7 +12,7 @@
 
 broPolicies=${BRO_SCRIPT_SOURCE_PATH}:${BRO_SCRIPT_SOURCE_PATH}/policy:${BRO_SCRIPT_SOURCE_PATH}/site
 
-broGenPolicies=${CMAKE_BINARY_DIR}/src
+broGenPolicies=${CMAKE_BINARY_DIR}/scripts
 
 installedPolicies=${BRO_SCRIPT_INSTALL_PATH}:${BRO_SCRIPT_INSTALL_PATH}/site