Enhancement - Path integration

- Implemented Path::operator (std::string) const, to provide an
  automatic cast to std::string for any Path, File or Directory.
- Made use of new cast in various code.
- Changed use of spaces in atoi () calls.
- Switched from std::string::data () to std::string::c_str () calls.

src/tests/directory.t.cpp

@@ -33,7 +33,7 @@ Context context;
 
 int main (int argc, char** argv)
 {
-  UnitTest t (20);
+  UnitTest t (21);
 
   // Directory (const File&);
   // Directory (const Path&);
@@ -55,6 +55,9 @@ int main (int argc, char** argv)
   Directory d5 = d4;
   t.is (d5.data, "/tmp/test_directory", "Directory::operator=");
 
+  // operator (std::string) const;
+  t.is ((std::string) d3, "/tmp", "Directory::operator (std::string) const");
+
   // virtual bool create ();
   t.ok (d5.create (), "Directory::create /tmp/test_directory");
   t.ok (d5.exists (), "Directory::exists /tmp/test_directory");