do not bother warning about marks left
on stack after syntax errors.
leave OCONV nodes in tree to avoid type errors
arising from multiple walks.
R=ken
OCL=30639
CL=30662
structtype{a:1, a:2}
maptypetype{"xx":1, "xx":2}
arraytypetype{5:1, 5:2}
2. bug in registerization concerning
alias of a struct and one of its elements
3. code optimization of struct.field
(which exposed bug in 2)
R=r
OCL=29315
CL=29315