Cleanup of redundant/useless header file inclusion.
ISC style lint, primarily for function declarations and standalone
comments -- ie, those that appear on a line without any code, which
should be written as follows:
/*
* This is a comment.
*/
<isc/boolean.h>, and now includes <isc/types.h>
instead of <isc/time.h>.
(does not need pthread.h because it *does* need isc/mutex.h, which
will be guaranteed to provide pthread.h)
