Please remove dependency on default:dry_shrub.

[Megaf]

moreblocks will not work if dry_shrub is removed or in other custom games that dont have dryshrubs.

2015-09-09 15:44:04: ERROR[Main]: ========== ERROR FROM LUA ===========
2015-09-09 15:44:04: ERROR[Main]: Failed to load and run script from 
2015-09-09 15:44:04: ERROR[Main]: /dev/shm/minetest/bin/../mods/moreblocks/init.lua:
2015-09-09 15:44:04: ERROR[Main]: /dev/shm/minetest/bin/../mods/moreblocks/redefinitions.lua:63: Attempt to override non-existent item default:dry_shrub
2015-09-09 15:44:04: ERROR[Main]: stack traceback:
2015-09-09 15:44:04: ERROR[Main]:   [C]: in function 'error'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../builtin/game/register.lua:324: in function 'override_item'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../mods/moreblocks/redefinitions.lua:63: in main chunk
2015-09-09 15:44:04: ERROR[Main]:   [C]: in function 'dofile'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../mods/moreblocks/init.lua:27: in main chunk
2015-09-09 15:44:04: ERROR[Main]: ======= END OF ERROR FROM LUA ========
2015-09-09 15:44:04: ERROR[Main]: Server: Failed to load and run /dev/shm/minetest/bin/../mods/moreblocks/init.lua
2015-09-09 15:44:04: ERROR[Main]: ModError: ModError: Failed to load and run /dev/shm/minetest/bin/../mods/moreblocks/init.lua
2015-09-09 15:44:04: ERROR[Main]: Error from Lua:
2015-09-09 15:44:04: ERROR[Main]: /dev/shm/minetest/bin/../mods/moreblocks/redefinitions.lua:63: Attempt to override non-existent item default:dry_shrub
2015-09-09 15:44:04: ERROR[Main]: stack traceback:
2015-09-09 15:44:04: ERROR[Main]:   [C]: in function 'error'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../builtin/game/register.lua:324: in function 'override_item'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../mods/moreblocks/redefinitions.lua:63: in main chunk
2015-09-09 15:44:04: ERROR[Main]:   [C]: in function 'dofile'
2015-09-09 15:44:04: ERROR[Main]:   /dev/shm/minetest/bin/../mods/moreblocks/init.lua:27: in main chunk