First prototype of new analyzer framework.

This is a larger internal change that moves the analyzer
infrastructure to a more flexible model where the available analyzers
don't need to be hardcoded at compile time anymore. While currently
they actually still are, this will in the future enable external
analyzer plugins. For now, it does already add the capability to
dynamically enable/disable analyzers from script-land, replacing the
old Analyzer::Available() methods.

There are three major parts going into this:

    - A new plugin infrastructure in src/plugin. This is independent
      of analyzers and will eventually support plugins for other parts
      of Bro as well (think: readers and writers). The goal is that
      plugins can be alternatively compiled in statically or loadead
      dynamically at runtime from a shared library. While the latter
      isn't there yet, there'll be almost no code change for a plugin
      to make it dynamic later (hopefully :)

    - New analyzer infrastructure in src/analyzer. I've moved a number
      of analyzer-related classes here, including Analyzer and DPM;
      the latter now renamed to Analyzer::Manager. More will move here
      later. Currently, there's only one plugin here, which provides
      *all* existing analyzers. We can modularize this further in the
      future (or not).

    - A new script interface in base/framework/analyzer. I think that
      this will eventually replace the dpm framework, but for now
      that's still there as well, though some parts have moved over.

I've also remove the dpd_config table; ports are now configured via
the analyzer framework. For exmaple, for SSH:

    const ports = { 22/tcp } &redef;

    event bro_init() &priority=5
        {
        ...
        Analyzer::register_for_ports(Analyzer::ANALYZER_SSH, ports);
        }

As you can see, the old ANALYZER_SSH constants have more into an enum
in the Analyzer namespace.

This is all hardly tested right now, and not everything works yet.
There's also a lot more cleanup to do (moving more classes around;
removing no longer used functionality; documenting script and C++
interfaces; regression tests). But it seems to generally work with a
small trace at least.

The debug stream "dpm" shows more about the loaded/enabled analyzers.

A new option -N lists loaded plugins and what they provide (including
those compiled in statically; i.e., right now it outputs all the
analyzers).

This is all not cast-in-stone yet, for some things we need to see if
they make sense this way. Feedback welcome.
Fixes for non-OSX.
Test-suite passes.

All tests pass with one exception: some Broxygen tests are broken
because dpd_config doesn't exist anymore. Need to update the mechanism
for auto-documenting well-known ports.
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?)
Updating cmake submodule.
Lots of cleanup and API documentation for the analyzer/* classes.

I've used the opportunity to also cleanup DPD's expect_connection()
infrastructure, and renamed that bif to schedule_analyzer(), which
seems more appropiate. One can now also schedule more than one
analyzer per connection.

TODOs:
        - "make install" is probably broken.
        - Broxygen is probably broken for plugin-defined events.
        - event groups are broken (do we want to keep them?)
        - parallel btest is broken, but I'm not sure why ...
          (tests all pass individually, but lots of error when running
          in parallel; must be related to *.bif restructuring).
        - Document API for src/plugin/*
        - Document API for src/analyzer/Analyzer.h
        - Document API for scripts/base/frameworks/analyzer
Removing legacy binpac analyzer for DNS and HTTP.
Removing the --use-binpac switch.
Removing all Analyzer::Available() methods.
Adding options Analyzer::disable_all to disable all analyzers at
startup.

One can then selectively enable the ones one wants inside a bro_init()
handler.
Giving analyzer/ its own CMakeLists.txt.

Also moving src/analyzer.bif to src/analyzer/analyzer.bif, along with
the infrastructure to build/incude bif code at other locations.

We should generally move to having per-directory CMakeLists.txt. I'll
convert the others over later.
Updating submodule.
Documenting Analyzer API, plus some cleanup.
Fixing test.
Removing some debugging output.
Porting syslog analyzer as another example.

The diff to this commit shows what "porting" involves ...

This also adds a small test for syslog.
Removing event groups.
A set of interface changes in preparation for merging into BinPAC++
branch.
Fixing ref counting bug.
More API documentation.