copied from https://fedorahosted.org/389/ticket/48038

need to be able to pass in functions to use for logging. functions should adhere as closely as possible to the syslog(3) interfaces. nunc-stans should use syslog by default. NSPR has a logging layer which we could use to abstract this. e.g. for testing, it will be desirable to use fprintf instead of syslog.

commit 5499cd4df5932a11072737c5ce78d300cfe52669