Include mg_decoration.h, mg_ore.h from emerge.cpp to fix warnings
Cleanup and (mostly) document util/string.h and (very) minor refactoring

Updated: Incorporated feedback from 'kahrl'
Updated: Moved MinetestApp::boolToCStr() from game.cpp into string.h renaming it bool_to_cstr()
Fix regression: mouse wheel couldn't scroll from last hotbar item to first
Merge remote-tracking branch 'minetest/master'

Conflicts:
	src/util/string.h