Fix double folding on e-mail headers

Ref: https://jira.ez.no/browse/EZP-23389

When setting a from/cc/bcc header with a very long name, and using a
charset different than the default one (e.g. `utf-8`), headers will be
double folded: once by `ezcMailTools::composeEmailAddress()`, and once
by `ezcMailHeaderFolder::foldAny()` (triggered from
`ezcMailPart::generateHeaders()`).

Line length won't change, but double line break will appear, making the
whole e-mail invalid.

This patch fixes it.
Merge pull request #32 from lolautruche/fixDoubleFold

Fix double folding on e-mail headers