gpg: Avoid name spaces clash with future sqlite versions.

* g10/sqlite.c: Rename to gpgsql.c.  Change function prefixes to
gpgsql_.
* g10/sqlite.h: Rename to gpgsql.h.
* g10/tofu.c: Adjust for changes.

We used for our own extensions symbols with an sqlite_ names prefix.
This may in theory lead to duplicated symbols but more important, it
is harder to understand what is from gpg and what is from libsqlite.

• Signed-off-by: Werner Koch <wk@gnupg.org>