Fixes regarding memory management

Fixes assorted issues identified by valgrind.

headers/modsecurity/collection/collection.h

@@ -39,6 +39,7 @@ namespace collection {
 
 class Collection {
  public:
+    virtual ~Collection() { };
     virtual void store(std::string key, std::string value) = 0;
 
     virtual bool storeOrUpdateFirst(const std::string &key,

headers/modsecurity/debug_log.h

@@ -36,7 +36,7 @@ class DebugLog {
         : m_debugLevel(-1),
         m_fileName("") { }
 
-    ~DebugLog();
+    virtual ~DebugLog();
 
     virtual void write(int level, const std::string &msg);
     bool isLogFileSet();

headers/modsecurity/rules_properties.h

@@ -103,7 +103,7 @@ class RulesProperties {
 */
     ~RulesProperties() {
         delete m_debugLog;
-    }
+    };
 
     std::vector<Rule *> rules[7];
     std::vector<Rule *> * getRulesForPhase(int phase) {