trac #15795 redone with ( ::)
trac #15795 line wrap
Fix the banner displayed by sage -h
Trac #15889: Make the banner displayed by sage -h look consistent with the main one

Before:
{{{
----------------------------------------------------------------------
│ Sage Version 6.2.beta3, Release Date: 2014-03-03                   │
┃ Warning: this is a prerelease version, and it may be unstable.     ┃
----------------------------------------------------------------------
}}}
After:
{{{
┌────────────────────────────────────────────────────────────────────┐
│ Sage Version 6.2.beta3, Release Date: 2014-03-03                   │
└────────────────────────────────────────────────────────────────────┘
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Warning: this is a prerelease version, and it may be unstable.     ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
}}}

URL: http://trac.sagemath.org/15889
Reported by: mmezzarobba
Ticket author(s): Marc Mezzarobba
Reviewer(s): Jeroen Demeyer
Trac #15795: fix VectorSpace.complement doc

There is a `::` missing.

URL: http://trac.sagemath.org/15795
Reported by: malb
Ticket author(s): Martin Albrecht
Reviewer(s): Frédéric Chapoton