mod_cgid: Improve handling of long AF_UNIX socket names (ScriptSock).

Dynamically allocate the AF_UNIX sockaddr based on the required filename size.
For some platforms (e.g., Solaris, OS X, FreeBSD), this allows longer
socket filenames to be used.

When the name is too long, the failure reporting is more consistent and a 
socket with truncated pathname is not left stranded.  The user still needs
to use ScriptSock to specify a shorter name.

An extra unlink() failure message may be generated when attempting to clean 
up the socket after a daemon initialization error; the message is surpressed 
for ENOTENT, but not for ENAMETOOLONG.

PR: 47037



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@765725 13f79535-47bb-0310-9956-ffa450edef68