Improve plugin.cmake dependency handling.

- Fix definition of _FOUND macro for lowercase dependencies.
- Support dependencies that are targets, tkae
  INTERFACE_INCLUDE_DIRECTORIES from their properties instead of looking
  for global variables.

cmake/plugin.cmake

@@ -207,7 +207,7 @@ macro (_check_plugin_deps _prefix _optional )
 
        if ( ${_optional} STREQUAL "TRUE"  )
 
-         if ( ${_VAL}_FOUND )
+           if ( ${_VAL}_FOUND OR ${_val}_FOUND)
 
            # Optional dependency found and recursive found, so add definition to enable it
            if ( ${_optional} STREQUAL "TRUE" )
@@ -276,6 +276,12 @@ macro (_check_plugin_deps _prefix _optional )
 
         if (${_val}_FOUND OR ${_VAL}_FOUND)
           foreach (_name ${_val} ${_VAL})
+            if (TARGET ${_name})
+                get_target_property(TARGET_INCDIRS ${_name} INTERFACE_INCLUDE_DIRECTORIES)
+                if (TARGET_INCDIRS)
+                    list (APPEND ${_prefix}_DEPS_INCDIRS ${TARGET_INCDIRS})
+                endif()
+            endif()
             if (DEFINED ${_name}_INCLUDE_PATH)
               list (APPEND ${_prefix}_DEPS_INCDIRS "${${_name}_INCLUDE_PATH}")
             endif ()