[preservefiles] Tidy up permissions code

- superfluous const
 - add default constructor
 - Add octal-string accessor to permissions

src/modules/preservefiles/permissions.cpp

@@ -21,17 +21,21 @@
 #include <QStringList>
 #include "permissions.h"
 
-Permissions::Permissions(QString p) :
+Permissions::Permissions() :
     m_username(),
     m_group(),
-    m_valid(true),
+    m_valid(false),
     m_value(0)
+{
+}
 
+
+Permissions::Permissions(QString p) : Permissions()
 {
     parsePermissions(p);
 }
 
-const void Permissions::parsePermissions(const QString& p) {
+void Permissions::parsePermissions(const QString& p) {
 
     QStringList segments = p.split(":");
 

src/modules/preservefiles/permissions.h

@@ -32,22 +32,25 @@ class Permissions
 
 public:
 
-/** Constructor
+    /** @brief Constructor
+     * 
      * Splits the string @p at the colon (":") into separate elements for 
      * <user>, <group>, and <value> (permissions), where <value> is returned as
      * an **octal** integer.
      */
     Permissions(QString p);
     
+    /** @brief Default constructor of an invalid Permissions. */
+    Permissions();
+
     bool isValid() const { return m_valid; }
     QString username() const { return m_username; }
     QString group() const { return m_group; }
     int value() const { return m_value; }
-
+    QString octal() const { return QString::number( m_value, 8 ); }
 
 private:
-
-    const void parsePermissions(QString const &p);
+    void parsePermissions(QString const &p);
 
     QString m_username;
     QString m_group;