Changes to whitespace in header field values break verification

[richanna]

Some header field values contain RWS, OWS, and/or BWS. Since the header field value canonicalization rules do not address whitespace, changes to it (e.g., removing OWS or BWS or replacing strings of RWS with a single space) can cause verification to fail.

[jricher]

Header canonicalization addresses whitespace from -02 onward in a way that should work.