Xpra: Ticket #1251: setup.py doesn't detect xvid

I downloaded the latest xvid codec (from http://svn.xvid.org/trunk), and built it and installed it in /usr/local. However, setup.py doesn't detect it.

PIT-MINTON-L7:~/src/Xpra/trunk/src$ python setup.py
setup.py
Xpra version 0.18.0
found pkg-config version: 0.29.1
build switches:
* enc_x264             : Y
* enc_x265             : Y
* xvid                 : N

[snip]
PIT-MINTON-L7:~/src/Xpra/trunk/src$ ls -las /usr/local/lib
total 13524
   0 drwxr-xr-x 1 root root     168 Jul  8 11:14 ./
   0 drwxr-xr-x 1 root root      76 Jun 15 08:20 ../
   0 drwxr-xr-x 1 root root      86 Aug 14  2015 F5Networks/
1624 -rw-r--r-- 1 root root 1659982 Jul  8 11:06 libx264.a
   4 lrwxrwxrwx 1 root root      14 Jul  8 11:06 libx264.so -> libx264.so.148*
1288 -rwxr-xr-x 1 root root 1317064 Jul  8 11:06 libx264.so.148*
5784 -rw-r--r-- 1 root root 5920738 Jul  8 11:14 libx265.a
   4 lrwxrwxrwx 1 root root      13 Jul  8 11:14 libx265.so -> libx265.so.87*
4820 -rwxr-xr-x 1 root root 4931952 Jul  8 11:14 libx265.so.87*
   0 drwxr-xr-x 1 root root      28 Jul  8 11:14 pkgconfig/
PIT-MINTON-L7:~/src/Xpra/trunk/src$ ls -las /usr/local/lib64
total 1768
   0 drwxr-xr-x 1 root root     122 Jul  8 11:40 ./
   0 drwxr-xr-x 1 root root      76 Jun 15 08:20 ../
1024 -rw-r--r-- 1 root root 1045330 Jul  8 11:40 libxvidcore.a
   4 lrwxrwxrwx 1 root root      18 Jul  8 11:21 libxvidcore.so -> libxvidcore.so.4.4
   4 lrwxrwxrwx 1 root root      18 Jul  8 11:21 libxvidcore.so.4 -> libxvidcore.so.4.4
 736 -rw-r--r-- 1 root root  751000 Jul  8 11:40 libxvidcore.so.4.4