builder target_scanner don't process Dir() nodes

[dragon512]

There are some other possible issues that appear to be affected by this problem. I made this issue as it is directly about the core issues of the scanner as this should be fixed independently. It may or may not fix some of the other issues that appear to be affected by this issue.

link to an example of this issue is here https://github.com/dragon512/scons-issues/tree/master/dir_scan

The root directory also contains a pipfile to help with quick environment setup of SCons