Print out a clearer error message when a `for` gets
used with the wrong type of iterator. Also fix spans on `for` loop
bodies, and suppress some more derived errors.
r=brson
Closes#3651
- Make `extern fn()` assignable to any closure type, rather than
a subtype.
- Remove unused int_ty_set and float_ty_set
- Refactor variable unification and make it more DRY
- Do fn sub/lub/glb on the level of fn_sig
- Rename infer::to_str::ToStr to infer::to_str::InferStr
- Capitalize names of various types
- Correct hashing of FnMeta
- Convert various records-of-fns into structs-of-fns. This is both
eliminating use of deprecated features and more forwards compatible
with fn reform.
r=pcwalton
Fixes#1896 which was never truly fixed, just masked.
The given tests would have failed had they used `~fn()` and
not `@fn()`. They now result in compilation errors.
Fixes#2978.
Necessary first step for #2202, #2263.
