Merge pull request #3329 from gavinandresen/syncdebug

mutex debugging routines: LocksHeld() and AssertLockHeld()

src/main.cpp

@@ -2176,6 +2176,8 @@ void PushGetBlocks(CNode* pnode, CBlockIndex* pindexBegin, uint256 hashEnd)
 
 bool ProcessBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBlockPos *dbp)
 {
+    AssertLockHeld("cs_main");
+
     // Check for duplicate
     uint256 hash = pblock->GetHash();
     if (mapBlockIndex.count(hash))