Encode::encode MIME-Header

The routine should not gobble up white space. This leads to all manner of bad
side-effects, such as encoded words starting and ending with spaces
where you'd want words surrounded by spaces, or encoding sequences of
words instead of single words.

Fix:

When constructing $especials, change the first line to read

  join( '|' => '\s', map { quotemeta( chr($_) ) }
---------------^^^^^