Add engine.gettext() and remove gettext() calls in guiFormspecMenu.cpp

* CURL support
* only download packages if they don't exist
* fixed download links (libvorbis and libogg)
* manual downloading if automatic downloading fails (only minetest and minetest_game)
* mingwm10.dll and openal_stripped.zip are downloaded automatically

Wireshark dissector: Add TOSERVER_RESPAWN and TOCLIENT_DEATHSCREEN, plus some failed assertion fix (well, hack).

minetestmapper: Fix the way ylist is computed, use cStringIO instead of rolling own Bytestream, remove some artifacts when drawing underground blocks, introduce a --drawunderground switch (defaults to of), 'blocknum' renamed to 'content'.