Instead of collecting all objects within a huge radius (which could be
a big value), just register each player that connects and give back the
current hold list.

Conflicts:
	src/script/lua_api/l_object.cpp

6b927229 Changed the default server step
from 0.05s to 0.1s

Texture names must now be escaped in formspec elements image[],
background[], image_button[], image_button_exit[].

Instead of special-case handling of texture loading (and unloading
which was missing) in guiFormSpecMenu.cpp, use the newly created
ISimpleTextureSource interface which is a minimal subset of
ITextureSource. There is an implementation of this interface
used by GUIEngine (MenuTextureSource).

Fix an off-by-one bug in unescape_string; it caused requests for a
texture called "\0".