BUG: TubeTK STATIC, even if itkTubeTK SHARED

itkTubeTK is a two-library system:

1) The include directory contains the itkTubeTK library which depends
on the TubeTK library. The itkTubeTK library is a high-quality ITK interface
(that can be wrapped for python) to the TubeTK library.

2) The src directory contains the TubeTK library which is an (ancient)
mix of ITK and non-ITK classes, functions, applications, and
examples.   It is poorly documented and inconsistent in style, but it
is rich in functionality :)

Regretfully the old TubeTK does not support being built as a shared
library.  So, even if itkTubeTK is being built shared, the underlying
TubeTK library will always be built static.

src/CMakeLists.txt

@@ -31,4 +31,6 @@ include( ObjectDocuments.cmake )
 include( Registration.cmake )
 include( Segmentation.cmake )
 
-itk_module_add_library( TubeTK ${TubeTK_SRCS} )
+add_library(TubeTK STATIC ${TubeTK_SRCS})
+itk_module_link_dependencies()
+itk_module_target(TubeTK)