Issue #404 Remove the underscore from the Go environment variable names

- This most likely won't fix the issue but they needed to be corrected
anyway; please verify the PATH environment variable is properly set in
the shell that you are running the build script in.
Issue #404 Bumping the required version of cmake

- find_package_handle_standard_args was failing with
'requires VERSION_VAR and GO_VERSION' in cmake 2.8
Change '. build.sh' to 'source build.sh' for more clarity.
Merge branch 'dev' of github.com:mozilla-services/heka into dev
Issue #399
Issue #354 don't allow an idle TCP connection to prevent Heka shutdown
Merge pull request #409 from mozilla-services/issue_354

Issue #354 don't allow an idle TCP connection to prevent Heka shutdown
Merge pull request #408 from mozilla-services/issue_399

Issue #399
Merge pull request #405 from mozilla-services/issue_404

Issue #404 Remove the underscore from the Go environment variable names
Merge branch 'dev' into features/diagnostics