Missing PF_LOCAL symbol in Solaris 10

The header files for Solaris 10 do not declare the symbol PF_LOCAL, used to specify Unix domain sockets as the "protocol family" for socket calls.

PF_LOCAL is the POSIX name for what BSD Unix called PF_UNIX. According to http://www.gnu.org/software/libc/manual/html_node/Address-Formats.html,

Although AF_LOCAL is mandated by POSIX.1g, AF_UNIX is portable to more systems ... (The same is true for PF_UNIX vs. PF_LOCAL)."

I verified that using PF_UNIX works around the problem on Solaris 10.

Suggest backport to 2.4 branch (optionally 2.2 as well).