Verify types when setting header

When a header is being set, verify that the type that's provided is
legal for the header that's been set. For example, the error channel's
type must be a MessageChannel or a String.

The method that performs type verification is protected so that it
can be overriden by sub-classes. It is expected that an overriding
method will call the super method.
Consider original headers in pattern-based removal

When headers are being removed based on pattern matching, both the
new header names and the original header names need to be matched
against the pattern. Previously, only new headers were being
considered resulting in any matching original headers not being
removed.