ENH: Add ITKHeaderTests target.
ENH: Add ITKHeaderTests target.

This target regenerates all the header tests and builds them.  This target is
useful when modifying the headers in modules.

This patch gives more control to the developer.  Four ways for rebuilding the
tests are now possible:

1) make ITKHeaderTests
  - Regenerates and rebuilds all header tests.
2) make ${module_name}HeaderTestClean && make
  - remove a given module's header test and rebuild the tests.
3) make clean && make
  - All the header tests will also be rebuilt in this case.
4) make rebuild_cache && make
  Currently rebuilding CMake cache causes the header tests to be rebuilt.  We
  may want to consider removing this behaviour after the toolkit has stabilized
  on 4.0 release.

Change-Id: I340438dc79819b8c3c1ad9252d4769d533b4515b

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