Add default includes for gtkdoc-mkdb
Add default includes for gtkdoc-mkdb

Fixes: NB#148188 (The required #include directives are not documented
       for Hildon)
Fixes: MB#6268 (The required #include directives are not documented
       for Hildon)

archlinuxarm-n900/libhildon,archlinuxarm-n900/libhildon,community-ssu/hildon,community-ssu/hildon,archlinuxarm-n900/libhildon,community-ssu/hildon