Relax token parsing when parsing header parameter values

Summary:
This allows for unquoted header parameter values with '/' character
to be parsed correctly instead of being split into two tokens. This
ensures compatibility with broken clients that generate unquoted header
paramters (like Kontact Enterprise35)

Reviewers: vkrause

Subscribers: KDE PIM

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D7918