* Fix setting the GSETTINGS_SCHEMA_DIR environment variable.
* Use g_value_take_boxed() instead of deprecated
g_value_set_boxed_take_ownership().
* Remove an unused variable.
* Clean up load_category() a bit.
This is required for gtkdoc-scangobj. So far it's much like it's been
before, the main differences are that source files are in two directories
from now on and the build process has two stages.