Fix expectations in Mail::Sendmail specs:

  Most examples weren't really testing the specific feature described,
but the whole implementation of #deliver! or other parts. This change
replace testing all arguments received by #call to testing what the
example description says.
  This avoid all test suddenly breaking when an unrelated part of code
is changed, and will also give better feedback when an example fail.
Revert safe shellescape method for Mail::Sendmail

FIXME: revert test about signaling end of options to sendmail

it 'asks sendmail to stop processing flags before giving destinations'