[SVN ci] MMD 39 - builtin MMDs as methods

[Leopold Toetsch]

This snippet:

.local pmc cl, l, r, d
cl = subclass "Integer", "AInt"
l = new "AInt"
r = new "AInt"
d = l."__add"(r) # d = n_add l, r

now works as expected.

These infix methods always return a new destination PMC so that the
function signature matches an HLLs signature for infix operations.

l."__add"(r, d) # wrong, d is ignored

The inplace variant is:

l."__i_add"(r) # l += r

leo