cmake: remove incorrect check for Boost

This variable isn't set until after the call to find_package. But the
REQUIRED arg to FIND_PACKAGE handles this for us.
Fix compile with srcdir != builddir
Ignore build and install dirs in Broker

Also, remove an IDE-specific ignore that belongs in user configuration
Add cmake option to enable Asio handler tracking

This will be very useful
trivial: cmake: lowercase sole uppercase command
trivial: cmake: style whitespace

We were previously completely inconsistent with our whitespace style.
So now I get to choose. Yay!
cmake: enforce min version of Boost
cmake: use find_package MODULE mode to find Boost

This looks simpler than the full version. Appeared in 2.8.8.
cmake: build recursively

I remember changing this myself; I have no idea why...
trivial: cmake: set warnings more naturally
Remove version.h

This extra header file is pointless and redundant. Store the version
in config.hpp instead.
cmake: check for Doxygen before calling it
Remove some help text from CMakeLists.

CMakeLists is NOT a tutorial:

* Polluting the build with instructions on how to use CMake is
  inconsiderate to users who know what they're doing.

* Developers know how to add config options. This isn't even
  something that's CMake-specific.
Use PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR

Slightly more proper; this will keep Broker building properly if
it becomes a subproject of a larger CMake project. (Which we might
very well want to do to allow building the whole distribution at
once.)
Add short instructions on adding cmake options for devs
Again target CMake 2.6

This is a courtesy to NCSU, who want to run on RHEL 6
Add note on setting CMake config options
Ignore the generated generator :)
Merge pull request #247 from scj7t4/cmake

CMake cleanup