Move check convenience target to regress.

This way, it works both top level and in regress.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1524dfe..06d8fc0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -179,7 +179,6 @@
   FILE_PERMISSIONS OWNER_READ OWNER_WRITE OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE
 )
 
-ADD_CUSTOM_TARGET(check COMMAND ${CMAKE_CTEST_COMMAND})
 
 # installation
 

regress/CMakeLists.txt

diff --git a/regress/CMakeLists.txt b/regress/CMakeLists.txt
index c406d30..7005b18 100644
--- a/regress/CMakeLists.txt
+++ b/regress/CMakeLists.txt
@@ -200,3 +200,5 @@
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR}/../lib
 	${CMAKE_CURRENT_SOURCE_DIR}/../src
 	${CMAKE_CURRENT_BINARY_DIR}/..)
+
+ADD_CUSTOM_TARGET(check COMMAND ${CMAKE_CTEST_COMMAND})