curses: integrate into posix tree.

* ext/curses/curses.c: Move from here...
* ext/posix/curses.c: ...to here.
* local.mk
* ext/posix/curses.c (luaopen_curses_c): Rename from this...
(luaopen_posix_curses): ...to this.
* lib/curses.lua: Adjust accordingly.
* local.mk (curses_cpath, ext_curses_curses_c_la_SOURCES)
(ext_curses_curses_c_la_LDFLAGS): Remove.
(std_cpath): Simplify accordingly.
(EXTRA_ext_posix_posix_la_SOURCES): Add ext/posix/curses.c.
(ex_posix_curses_la_LDFLAGS, ext_posix_posix_la_LDFLAGS): Add
$(CURSES_LIB).
(posix_submodules): Add ext/posix/curses.la.
* ext/posix/curses.c (luaopen_posix_curses): Add a version
entry to the returned table to match other posix modules.
* build-aux/make_lcurses_doc.pl: Adjust accordingly.
* ext/posix/posix.c: Include curses.c module.
* configure.ac (WANTEDLIBS, WANTEDLUA): Remove. Treat it like
other posix modules with no OS support.
* local.mk (dist_lua_DATA, luaexec_LTLIBRARIES): Adjust
accordingly.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>