http_driver bug-fix -- the keepalive timer should not be started in the ctor of the driver object, but rather only after the accept-connection event has occured.

also, adding extra verbosity to the ssl-related handshake errors in http_driver.

custom_env.sh and BSDmakefile -- censoc-centric includes are now treated as any other 3rd party lib: via the environment variable/shell substitution/setting (as opposed to explicit -I directive in the BSDmakefile).