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/file.t.cpp

@@ -33,7 +33,7 @@ Context context;
 
 int main (int argc, char** argv)
 {
-  UnitTest t (5);
+  UnitTest t (6);
 
   File::write ("/tmp/file.t.txt", "This is a test\n");
   File f6 ("/tmp/file.t.txt");
@@ -41,6 +41,9 @@ int main (int argc, char** argv)
   t.ok (f6.mode () & S_IRUSR, "File::mode /tmp/file.t.txt good");
   t.ok (File::remove ("/tmp/file.t.txt"), "File::remove /tmp/file.t.txt good");
 
+  // operator (std::string) const;
+  t.is ((std::string) f6, "/tmp/file.t.txt", "File::operator (std::string) const");
+
   t.ok (File::create ("/tmp/file.t.create"), "File::create /tmp/file.t.create good");
   t.ok (File::remove ("/tmp/file.t.create"), "File::remove /tmp/file.t.create good");