go/types: refers to go/constant as exact

[dvyukov]

go/types docs:
http://tip.golang.org/pkg/go/types
periodically refer to a package exact. For example:

Constant folding computes the exact constant value (exact.Value) for every expression

and:

type TypeAndValue struct {
    Type  Type
    Value exact.Value
    // contains filtered or unexported fields
}

This is very confusing. There is no package exact.
I understand this was introduced during refactoring, but the cost of confused users is higher than the cost of sed invocation.

[griesemer]

Since we're late in the release cycle I'll address the documentation (comment) issue for now.

[gopherbot]

CL https://golang.org/cl/13051 mentions this issue.