Sanity checks for estimates

Require at least 11 samples before giving fee/priority estimates.

And have wallet-created transactions go throught the fee-sanity-check
code path.

src/main.h

@@ -452,7 +452,7 @@ public:
     int GetDepthInMainChain() const { CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet); }
     bool IsInMainChain() const { CBlockIndex *pindexRet; return GetDepthInMainChainINTERNAL(pindexRet) > 0; }
     int GetBlocksToMaturity() const;
-    bool AcceptToMemoryPool(bool fLimitFree=true);
+    bool AcceptToMemoryPool(bool fLimitFree=true, bool fRejectInsaneFee=true);
 };