Propagate details of ICAP errors happened after adapted HTTP header creation.

Propagate details of ICAP errors happened after adapted HTTP header creation.

We used to update the virgin HTTP request with error details even after REQMOD
resulted in creation of a new/adapted HTTP request object. When the client
side replaced the old/virgin request headers with the new adapted request
object, the error details were lost and %err_detail was not logged to the
transaction log.

This is one more place where a Master Transaction object (with a shared error
detail field) should be extracted from the HttpRequest and persist throughout
the HTTP transaction lifetime.