Partial: Sanitize assert usage and refuse to compile with NDEBUG.

There were quite a few places where assert() was used with side effects,
 making operation with NDEBUG non-functional.  This commit fixes all the
 cases I know about, but also adds an  #error on NDEBUG because the code
 is untested without assertions and may still have vulnerabilities if
 used without assert.

Conflicts:
	src/key.cpp
	src/main.cpp
	src/wallet.cpp

Rebased-from: 2e0c4da3fb1ce78dca1b3db723cf095a94f2f371 0.8.x

src/main.cpp

@@ -18,6 +18,10 @@
 using namespace std;
 using namespace boost;
 
+#if defined(NDEBUG)
+# error "Litecoin cannot be compiled without assertions."
+#endif
+
 //
 // Global state
 //
@@ -1343,12 +1347,14 @@ unsigned int CTransaction::GetP2SHSigOpCount(CCoinsViewCache& inputs) const
 
 void CTransaction::UpdateCoins(CValidationState &state, CCoinsViewCache &inputs, CTxUndo &txundo, int nHeight, const uint256 &txhash) const
 {
+    bool ret;
     // mark inputs spent
     if (!IsCoinBase()) {
         BOOST_FOREACH(const CTxIn &txin, vin) {
             CCoins &coins = inputs.GetCoins(txin.prevout.hash);
             CTxInUndo undo;
-            assert(coins.Spend(txin.prevout, undo));
+            ret = coins.Spend(txin.prevout, undo);
+            assert(ret);
             txundo.vprevout.push_back(undo);
         }
     }