Change set_signals() to use sigaction() for setup of signal handlers.

sigaction() has the proper effect of blocking the signal until the
return from the handler.
Reviewed by: Ben Laurie, Paul Richards


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@77247 13f79535-47bb-0310-9956-ffa450edef68