script: move CScriptID to standard.h and add a ctor for creating them from CScripts

This allows for a reversal of the current behavior.

This:
CScript foo;
CScriptID bar(foo.GetID());

Becomes:
CScript foo;
CScriptID bar(foo);

This way, CScript is no longer dependent on CScriptID or Hash();

src/script/compressor.cpp

@@ -4,6 +4,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "compressor.h"
+#include "script/standard.h"
 
 bool CScriptCompressor::IsToKeyID(CKeyID &hash) const
 {

src/script/compressor.h

@@ -8,6 +8,8 @@
 
 #include "script/script.h"
 
+class CScriptID;
+
 /** Compact serializer for scripts.
  *
  *  It detects common cases and encodes them much more efficiently.

src/script/script.h

@@ -610,12 +610,6 @@ public:
         }
         return str;
     }
-
-    CScriptID GetID() const
-    {
-        return CScriptID(Hash160(*this));
-    }
-
     void clear()
     {
         // The default std::vector::clear() does not release memory.

src/script/standard.cpp

@@ -14,6 +14,8 @@ using namespace std;
 
 typedef vector<unsigned char> valtype;
 
+CScriptID::CScriptID(const CScript& in) : uint160(in.size() ? Hash160(in.begin(), in.end()) : 0) {}
+
 const char* GetTxnOutputType(txnouttype t)
 {
     switch (t)

src/script/standard.h

@@ -13,6 +13,15 @@
 
 class CScript;
 
+/** A reference to a CScript: the Hash160 of its serialization (see script.h) */
+class CScriptID : public uint160
+{
+public:
+    CScriptID() : uint160(0) {}
+    CScriptID(const CScript& in);
+    CScriptID(const uint160& in) : uint160(in) {}
+};
+
 static const unsigned int MAX_OP_RETURN_RELAY = 40;      // bytes
 
 // Mandatory script verification flags that all new blocks must comply with for