Okay, from what I've read on the Nvidia site, there are special headers, but you don't need them unless you want to use special NV extensions. So I guess my question is about programs finding the mesa headers:
# pkg-config --cflags --libs gl
-lGL
# pkg-config --modversion gl
9.1.4
# apt-cache policy mesa-common-dev
mesa-common-dev:
Installed: 9.1.4-1
Candidate: 9.1.4-1
Version table:
*** 9.1.4-1 0
500 http://ftp.us.debian.org/debian/ unstable/main amd64 Packages
100 /var/lib/dpkg/status