consolidate code related to sig_coredump

a note on perchild:
  perchild exception handling was busted before this and is still busted
  the problem I noticed was that a client that exposes a segfault never
  gets its connection dropped and the parent never notices that the
  child process that segfaulted hasexited


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99312 13f79535-47bb-0310-9956-ffa450edef68