in fact mod_so.c is likely your issue:
http://httpd.apache.org/docs/1.3/mod/mod_so.html
Status: Base (Windows); Experimental (Unix)
I haven't even got that on my system, so you definitely got that sucka from http-devel yum install...
and plus, fwiw, I would never yum -y
anything - I like to see what yum is going to add/remove so I can opt out... with -y, you're giving yum a wild card to trash your system ;)