Give testnet it's own alert key.

src/alert.cpp

@@ -16,6 +16,9 @@ using namespace std;
 map<uint256, CAlert> mapAlerts;
 CCriticalSection cs_mapAlerts;
 
+static const char* pszMainKey = "04fc9702847840aaf195de8442ebecedf5b095cdbb9bc716bda9110971b28a49e0ead8564ff0db22209e0374782c093bb899692d524e9d6a6956e7c5ecbcd68284";
+static const char* pszTestKey = "04302390343f91cc401d56d68b123028bf52e5fca1939df127f63c6467cdf9c8e2c14b61104cf817d0b780da337893ecc4aaff1309e536162dabbdb45200ca2b0a";
+
 void CUnsignedAlert::SetNull()
 {
     nVersion = 1;
@@ -139,7 +142,7 @@ bool CAlert::RelayTo(CNode* pnode) const
 bool CAlert::CheckSignature() const
 {
     CKey key;
-    if (!key.SetPubKey(ParseHex("04fc9702847840aaf195de8442ebecedf5b095cdbb9bc716bda9110971b28a49e0ead8564ff0db22209e0374782c093bb899692d524e9d6a6956e7c5ecbcd68284")))
+    if (!key.SetPubKey(ParseHex(fTestNet ? pszTestKey : pszMainKey)))
         return error("CAlert::CheckSignature() : SetPubKey failed");
     if (!key.Verify(Hash(vchMsg.begin(), vchMsg.end()), vchSig))
         return error("CAlert::CheckSignature() : verify signature failed");