standardise amagic method naming

standardise amagic method naming

Some amagic-related macros take the full method enumeration name,
(e.g. "add_amg"); while others "helpfully" allow you to pass a shortened
version, ("add"), and do a CAT2(meth,_amg) behind the scenes.

Standardise on passing the full name; this makes it less confusing and
allows you to grep for the enumeration name in the source.

It updates two macros to accept full enumeration names: tryAMAGICunTARGET
(which isn't used outside the core apparently), and AMG_CALLun, which is
replaced by a new AMG_CALLunary (since AMG_CALLun is used outside the
core).