Move 'dlg' submodule to `subprojects` directory.

This is for future changes with Meson, which doesn't allow a
different name for its `subprojects` directory.  Having both a
`submodules` and a `subprojects` directory is confusing.

* .gitmodules, autogen.sh (copy_submodule_files, DLG_INC_DIR,
DLG_SRC_DIR): Updated.

* builds/toplevel.mk (<top-level>, do-dist),
builds/windows/vc2010/script.bat: Updated.

* src/tools/no-copyright: Updated.
7 files changed