decrase minblockGasLimit to 5000 for frontier

libethcore/Common.cpp

@@ -61,7 +61,7 @@ Network resetNetwork(Network _n)
 {
 	c_network = _n;
 	c_maximumExtraDataSize = c_network == Network::Olympic ? 1024 : 32;
-	c_minGasLimit = c_network == Network::Turbo ? 100000000 : 125000;
+	c_minGasLimit = c_network == Network::Turbo ? 100000000 : 5000;
 	c_gasLimitBoundDivisor = 1024;
 	c_minimumDifficulty = 131072;
 	c_difficultyBoundDivisor = 2048;