Fix from quote headers regexes

[kipit]

This fix two things for "From:" quote headers.

Improve regex for edge case

We had to handle this kind of weird email (note that the begining of the content are newlines):

From: foo <foo@example.com>

My email is <foo@example.com>

We the actual regex, this lead to messup the content of the second fragment, instead of getting:

From: foo <foo@example.com>

My email is <foo@example.com>

we get

From: foo <foo@example.com> My email is <foo@example.com>

ATM, a simple solution is to consider that this kind of header cannot span over multiple lines. This is the solution we offer in this PR.

Fix escaping of '['**

Working on this fix we encounter a case that caught up to our eye that an escaping was missing.

[kipit]

@willdurand any problem with these modifications?

[willdurand]

nope, I forgot this PR.. Thanks!