When you try to build git v1.7.0.6 on Red Hat Enterprise Linux 3, you get an error:
In file included from /usr/include/openssl/ssl.h:179,
from git-compat-util.h:139,
from builtin.h:4,
from fast-import.c:147:
/usr/include/openssl/kssl.h:72:18: krb5.h: No such file or directory
I have the answer to this, and I'm just posting it here for posterity.