Disable microthreading. A user reported that the command

   ./twsearch --scramblealg "R2 U2 R2 U2 D2 R2 U2 L2" --moves R2,U2,L2,D2 --writeprunetables never samples/3x3x3.tws
would give nondetermistic results, and it looks like microthreading is to blame.
This is a temporary patch until we fix it more properly.

src/cpp/twsearch.cpp

@@ -73,7 +73,7 @@ void reseteverything() {
 #else
  numthreads = 1;
 #endif
- requesteduthreading = 4;
+ requesteduthreading = 1;
  verbose = 1;
  start = walltime();
  quarter = 0;
@@ -130,8 +130,8 @@ static intopt intopts[] = {
  "num Use search-based canonical sequences to the given depth.", &ccount,
  0, 100},
  {"-t", "num Use this many threads.", &numthreads, 1, MAXTHREADS},
-  {"--microthreads", "num Use this many microthreads on each thread.",
-  &requesteduthreading, 1, MAXMICROTHREADING},
+// {"--microthreads", "num Use this many microthreads on each thread.",
+// &requesteduthreading, 1, MAXMICROTHREADING},
  {"--orientationgroup",
  "num Treat adjacent piece groups of this size as\n"
  "orientations.",