Build fixed, goofed up some CMake

Forgot that CMake vars set to PARENT_SCOPE will still vanish if that
parent scope goes...out of scope.  LMDB vars elevated one more scope to
compensate for moving db_drivers/ into external/

external/CMakeLists.txt

@@ -99,3 +99,7 @@ else()
 endif()
 
 add_subdirectory(db_drivers)
+set(LMDB_STATIC ${LMDB_STATIC} PARENT_SCOPE)
+set(LMDB_INCLUDE ${LMDB_INCLUDE} PARENT_SCOPE)
+set(LMDB_LIBRARY ${LMDB_LIBRARY} PARENT_SCOPE)
+set(LMDB_LIBRARY_DIRS ${LMDB_LIBRARY_DIRS} PARENT_SCOPE)