restore SpecFrom<T, TrustedLen<Item=T>> specialization by nesting specializations
restore SpecFrom<T, TrustedLen<Item=T>> specialization by nesting
specializations

aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust