BUG: Fix windows command line escape for empty arg
BUG: Fix windows command line escape for empty arg

On Windows the KWSys System package generates escapes for command-line
arguments.  This fix enables quoting of the empty string as an argument.
This also adds a test to pass an empty argument to a custom command.

spinicist/ITK,hinerm/ITK,rhgong/itk-with-dom,zachary-williamson/ITK,blowekamp/ITK,rhgong/itk-with-dom,jcfr/ITK,eile/ITK,eile/ITK,wkjeong/ITK,hjmjohnson/ITK,daviddoria/itkHoughTransform,CapeDrew/DCMTK-ITK,LucHermitte/ITK,vfonov/ITK,CapeDrew/DCMTK-ITK,hendradarwin/ITK,heimdali/ITK,vfonov/ITK,paulnovo/ITK,InsightSoftwareConsortium/ITK,blowekamp/ITK,PlutoniumHeart/ITK,fuentesdt/InsightToolkit-dev,zachary-williamson/ITK,daviddoria/itkHoughTransform,itkvideo/ITK,fedral/ITK,hjmjohnson/ITK,paulnovo/ITK,jcfr/ITK,hjmjohnson/ITK,PlutoniumHeart/ITK,blowekamp/ITK,hjmjohnson/ITK,ajjl/ITK,biotrump/ITK,daviddoria/itkHoughTransform,spinicist/ITK,jcfr/ITK,LucasGandel/ITK,daviddoria/itkHoughTransform,blowekamp/ITK,vfonov/ITK,vfonov/ITK,biotrump/ITK,LucasGandel/ITK,jcfr/ITK,thewtex/ITK,BRAINSia/ITK,hinerm/ITK,zachary-williamson/ITK,paulnovo/ITK,LucHermitte/ITK,cpatrick/ITK-RemoteIO,BlueBrain/ITK,PlutoniumHeart/ITK,paulnovo/ITK,LucasGandel/ITK,malaterre/ITK,hinerm/ITK,malaterre/ITK,malaterre/ITK,PlutoniumHeart/ITK,CapeDrew/DCMTK-ITK,msmolens/ITK,ajjl/ITK,richardbeare/ITK,itkvideo/ITK,zachary-williamson/ITK,spinicist/ITK,hendradarwin/ITK,daviddoria/itkHoughTransform,hjmjohnson/ITK,thewtex/ITK,PlutoniumHeart/ITK,jmerkow/ITK,GEHC-Surgery/ITK,fbudin69500/ITK,daviddoria/itkHoughTransform,hinerm/ITK,cpatrick/ITK-RemoteIO,Kitware/ITK,paulnovo/ITK,atsnyder/ITK,fbudin69500/ITK,richardbeare/ITK,cpatrick/ITK-RemoteIO,cpatrick/ITK-RemoteIO,LucHermitte/ITK,heimdali/ITK,InsightSoftwareConsortium/ITK,atsnyder/ITK,itkvideo/ITK,LucHermitte/ITK,jmerkow/ITK,blowekamp/ITK,ajjl/ITK,jmerkow/ITK,CapeDrew/DITK,eile/ITK,ajjl/ITK,LucHermitte/ITK,zachary-williamson/ITK,richardbeare/ITK,stnava/ITK,fbudin69500/ITK,daviddoria/itkHoughTransform,LucasGandel/ITK,paulnovo/ITK,biotrump/ITK,fuentesdt/InsightToolkit-dev,GEHC-Surgery/ITK,jmerkow/ITK,jmerkow/ITK,hjmjohnson/ITK,spinicist/ITK,thewtex/ITK,biotrump/ITK,vfonov/ITK,stnava/ITK,hinerm/ITK,hjmjohnson/ITK,malaterre/ITK,rhgong/itk-with-dom,CapeDrew/DCMTK-ITK,heimdali/ITK,fuentesdt/InsightToolkit-dev,vfonov/ITK,BlueBrain/ITK,malaterre/ITK,thewtex/ITK,fedral/ITK,InsightSoftwareConsortium/ITK,rhgong/itk-with-dom,zachary-williamson/ITK,fuentesdt/InsightToolkit-dev,cpatrick/ITK-RemoteIO,fbudin69500/ITK,eile/ITK,msmolens/ITK,heimdali/ITK,rhgong/itk-with-dom,BRAINSia/ITK,BRAINSia/ITK,itkvideo/ITK,hendradarwin/ITK,BlueBrain/ITK,spinicist/ITK,spinicist/ITK,vfonov/ITK,jcfr/ITK,jcfr/ITK,paulnovo/ITK,hendradarwin/ITK,zachary-williamson/ITK,hendradarwin/ITK,cpatrick/ITK-RemoteIO,InsightSoftwareConsortium/ITK,CapeDrew/DCMTK-ITK,atsnyder/ITK,spinicist/ITK,atsnyder/ITK,Kitware/ITK,eile/ITK,CapeDrew/DITK,GEHC-Surgery/ITK,richardbeare/ITK,BlueBrain/ITK,stnava/ITK,Kitware/ITK,stnava/ITK,BlueBrain/ITK,Kitware/ITK,biotrump/ITK,itkvideo/ITK,msmolens/ITK,msmolens/ITK,wkjeong/ITK,ajjl/ITK,BRAINSia/ITK,atsnyder/ITK,cpatrick/ITK-RemoteIO,PlutoniumHeart/ITK,BRAINSia/ITK,fbudin69500/ITK,Kitware/ITK,fbudin69500/ITK,blowekamp/ITK,vfonov/ITK,wkjeong/ITK,atsnyder/ITK,GEHC-Surgery/ITK,heimdali/ITK,blowekamp/ITK,atsnyder/ITK,LucasGandel/ITK,CapeDrew/DCMTK-ITK,ajjl/ITK,hinerm/ITK,atsnyder/ITK,InsightSoftwareConsortium/ITK,hendradarwin/ITK,vfonov/ITK,heimdali/ITK,rhgong/itk-with-dom,LucasGandel/ITK,eile/ITK,cpatrick/ITK-RemoteIO,itkvideo/ITK,BlueBrain/ITK,fuentesdt/InsightToolkit-dev,CapeDrew/DITK,CapeDrew/DCMTK-ITK,msmolens/ITK,wkjeong/ITK,malaterre/ITK,jcfr/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,GEHC-Surgery/ITK,richardbeare/ITK,stnava/ITK,fedral/ITK,fbudin69500/ITK,GEHC-Surgery/ITK,zachary-williamson/ITK,LucasGandel/ITK,biotrump/ITK,GEHC-Surgery/ITK,BRAINSia/ITK,GEHC-Surgery/ITK,BRAINSia/ITK,CapeDrew/DCMTK-ITK,thewtex/ITK,ajjl/ITK,msmolens/ITK,Kitware/ITK,LucHermitte/ITK,biotrump/ITK,stnava/ITK,hinerm/ITK,eile/ITK,richardbeare/ITK,paulnovo/ITK,wkjeong/ITK,msmolens/ITK,malaterre/ITK,CapeDrew/DITK,itkvideo/ITK,jmerkow/ITK,fuentesdt/InsightToolkit-dev,CapeDrew/DITK,wkjeong/ITK,fedral/ITK,zachary-williamson/ITK,itkvideo/ITK,heimdali/ITK,fedral/ITK,stnava/ITK,jmerkow/ITK,CapeDrew/DCMTK-ITK,thewtex/ITK,malaterre/ITK,daviddoria/itkHoughTransform,fedral/ITK,malaterre/ITK,fuentesdt/InsightToolkit-dev,rhgong/itk-with-dom,fedral/ITK,BlueBrain/ITK,ajjl/ITK,fuentesdt/InsightToolkit-dev,blowekamp/ITK,wkjeong/ITK,hinerm/ITK,heimdali/ITK,CapeDrew/DITK,fuentesdt/InsightToolkit-dev,CapeDrew/DITK,msmolens/ITK,CapeDrew/DITK,itkvideo/ITK,biotrump/ITK,LucasGandel/ITK,fedral/ITK,BlueBrain/ITK,jcfr/ITK,wkjeong/ITK,stnava/ITK,spinicist/ITK,InsightSoftwareConsortium/ITK,thewtex/ITK,eile/ITK,daviddoria/itkHoughTransform,hinerm/ITK,rhgong/itk-with-dom,atsnyder/ITK,fbudin69500/ITK,hendradarwin/ITK,LucHermitte/ITK,Kitware/ITK,jmerkow/ITK,stnava/ITK,eile/ITK,PlutoniumHeart/ITK,spinicist/ITK,CapeDrew/DITK,PlutoniumHeart/ITK,LucHermitte/ITK,hendradarwin/ITK