C++ API changes+fixes:

- context is now a pointer to make sure there's only one all the time
- fixed a couple of double free's
- some minor bug fixes

bindings/cpp/vault++.h

@@ -46,13 +46,13 @@ namespace pcp {
   class Vault {
   private:
     vault_t *V;
-    PcpContext PTX;
+    PcpContext *PTX;
 
   public:
     // constructors
     Vault();
-    Vault(PcpContext &P);
-    Vault(PcpContext &P, std::string filename);
+    Vault(PcpContext *P);
+    Vault(PcpContext *P, std::string filename);
 
     // destructor
     ~Vault();