[Mutt] #2988: Mutt should recognize tab (width)

[Mutt <fleas@xxxxxxxx>]

#2988: Mutt should recognize tab (width)

 In mutt_strwidth() there's a check for printable chars which excludes tab
 chars resulting in a width of 1. However, this is likely not the display
 width resulting in wrong wrapping and possibly other undesired effects.

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Ticket URL: <http://dev.mutt.org/trac/ticket/2988>