Need to distinguish mget and get

[rainwoodman]

If we want to support the following syntax, then we need
to distinguish mget (metaget) and get:

x = {}
x.update({})

. shall translate to mget, which first check the meta dict;

[] shall translate get, which will first check the dict

[rainwoodman]

This is now supported. But with a quirk:

'update' in x is false, but x['update'] returns a function

[rainwoodman]

Another way to deal with this is that:

• . will bound the function
• [] does not bound the function
• {} creates a raw dict.