Fixed a bug in b15 reported by github user HenryHu.  This doesn't seem to affect the Linux version, but I wonder if it's related to the hang on Windows.  The fix has been pushed to git in https://github.com/dave-andersen/fastrie/commit/79e21cecb9bea07caac30c6a6b46735f558faee8

(It's a one-line fix that should not mess up Gatra's current effort at porting to stratum)

I've put a temporary alpha test binary in http://www.cs.cmu.edu/~dga/crypto/ric/alpha/xptminer-sse4-b15.exe

if someone with windows wants to see if that one actually works or not.  It probably doesn't, but it's worth checking.

Thanks to HenryHu for the report and precise identification of the bug!

(If anyone tests it and notices that this actually fixes a real bug on Linux, LMK and I'll push out a quick b16 build)