FreeBSD support of build infrastructure

This adds FreeBSD support to osquery's build system, and only does it.  It could be the preliminary work of porting osquery to FreeBSD, and enables more people start to work on it without solving tedious build issues.

Build process:

1) Install dependencies:

autoconf
automake
bison
boost
cmake
gflags
git
glog
gmake
libtool
libunwind
rocksdb
snappy
thrift
thrift-cpp

tools/provision.sh did not install build packages for FreeBSD, just skips them.

2)
For now, the implementations of following tables do not exist (yet):

osquery/tables/specs/x/groups.table
osquery/tables/specs/x/passwd_changes.table
osquery/tables/specs/x/process_envs.table
osquery/tables/specs/x/process_open_files.table
osquery/tables/specs/x/processes.table
osquery/tables/specs/x/routes.table
osquery/tables/specs/x/users.table

By removing them temporarily, osquery can be built under FreeBSD with just `gmake`.
I think that, until we have the ability to support both static AND dynamic linking of dependencies, we should bias towards dynamic linking. Also, writing "libsnappy.so" in that list is functionally equivalent to writing "snappy". The only reason why one would specify the full filename is so that you can mandate that CMake grabs the static lib. 

IMO, we should link everything dynamically OR make the decision to support statically linked bins by default (which I have other issues with). Right now we're kind of in this wishy washy in between state and it's seventeen kinds of messed up.