improve the scripts for building unit tests:

* support unsupported/
* use egrep instead of grep, properly escape special chars.

CMakeLists.txt

@@ -152,6 +152,9 @@ add_subdirectory(doc EXCLUDE_FROM_ALL)
 
 include(CTest)
 enable_testing() # must be called from the root CMakeLists, see man page
+include(EigenTesting)
+ei_init_testing()
+
 if(EIGEN_LEAVE_TEST_IN_ALL_TARGET)
   add_subdirectory(test) # can't do EXCLUDE_FROM_ALL here, breaks CTest
 else()
@@ -164,6 +167,7 @@ add_subdirectory(demos EXCLUDE_FROM_ALL)
 
 add_subdirectory(blas EXCLUDE_FROM_ALL)
 
+# must be after test and unsupported, for configuring buildtests.in
 add_subdirectory(scripts EXCLUDE_FROM_ALL)
 
 # TODO: consider also replacing EIGEN_BUILD_BTL by a custom target "make btl"?