image/jpeg: TestVeryLargeImageWithShortData failing with "out of memory" on openbsd/386

[mdempsky]

E.g., http://build.golang.org/log/d00e51284a1e3a852a54fba3abed6f945e862866
Seems introduced by 72e867e (cc @nigeltao).
Judging by runtime.makeslice(0x81646a0, 0x25c00000, 0x0, 0x25c00000, 0x0, 0x0, 0x0, 0x0) in the stack trace, it looks like it's trying to allocate a 633MB byte buffer and failing?

I can look into why it's failing (maybe something easily fixable), but probably easiest for now to disable on openbsd/386?