Fix configure and makefiles so build process is more robust

Concurrency kit is installed by default into /usr/include/ck
so pkg-config is used to find the headers and libs instead
of overriding the CK location using --prefix=/usr.

When Riemann was enabled during the build process Google
Protocol Buffers was being incorrectly linked to the ganglia agent
eventhough it isn't used. This should now be fixed.
Merge pull request #133 from satterly/master

Fix configure and makefiles so build process is more robust