Expand this.promiser for some attributes in files promises.

Supported are attributes in body classes and log-attributes in
body action, as well as the previously supported transformer.

Addresses the highest priority items left in Redmine #1554.
We should really have a 
```
char *BufferDisembowel(Buffer *b)
{
    char * ans = b->buffer;
    free(b);
    return ans;
}
```
to save gratuitous copying in cases like this.