Don't bypass scan_content() when expanding pseudoheaders.

Don't bypass scan_content() when expanding pseudoheaders.

expand_pseudoheader() would avoid the call to scan_content() in order
to inhibit use of quoted-printable for text content.  Removed that;
the user still has control over the use of quoted-printable via
-maxunencoded.  Though now, lines over 998 bytes long will always
be encoded.