Add execdir primary to dicomfind.
Add execdir primary to dicomfind.

This primary is very useful when the directory names have spaces,
because it ensures that the executed command will not see those
spaces.  Also, if a series has been duplicated (the same series
appears in multiple directories), then each duplicate will be
independently executed upon.  Conversely, a series that is split
across directories will be executed in parts.

dgobbi/vtk-dicom,dgobbi/vtk-dicom,dgobbi/vtk-dicom,hendradarwin/vtk-dicom,hendradarwin/vtk-dicom,hendradarwin/vtk-dicom