[krbdev.mit.edu #7860] libdb2 tests hang

[Greg Hudson via RT]

Please test this candidate fix:

https://github.com/greghudson/krb5/commits/circleq

It works for me with gcc 4.8.1 and -O2.  I still want to do more analysis 
(probably with Tom's help) on whether CIRCLEQ and TAILQ violate strict 
aliasing.  But we use TAILQ in several other parts of the code and don't 
use CIRCLEQ anywhere else, so switching from CIRCLEQ to TAILQ is probably 
a reasonable step regardless.