[sql] Import reference version of SQLite 3.8.7.4.

third_party/sqlite/sqlite-src-3080704/test/threadtest1.c

 /*
 ** 2002 January 15
 **
 ** The author disclaims copyright to this source code.  In place of
 ** a legal notice, here is a blessing:
 **
 **    May you do good and not evil.
 **    May you find forgiveness for yourself and forgive others.
 **    May you share freely, never taking more than you give.
 **
@@ skipping 269 matching lines @@
     pthread_cond_wait(&sig, &lock);
   }
   pthread_mutex_unlock(&lock);
   for(i=0; i<n; i++){
     char zBuf[200];
     sprintf(zBuf, "testdb-%d", (i+1)/2);
     unlink(zBuf);
   }
   return 0;
 }