Cope with headers formatted as Name:\r\n\tValue

[manu0401]

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Without this change, the canonization of a header like Name:\r\n\tValue wrongly leaves a space after the colon, and causing the signature to be rejected.

[rhansen]

@manu0401 This was fixed on the develop branch over 5 years ago by commit a65442161a6e59de49b3db9091754174e363c392. It's unfortunate there hasn't been a release since then (other than betas).

Also see:

• joyent/pkgsrc#285
• NetBSD/pkgsrc#78
• https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=55171