Stopping vim from auto-indenting

[mdevin <mdevin@ozemail.com.au>]

When I use vim to edit a file, then copy and paste some text into this
file, the text gets automatically indented more than it should.  Take
the following example:
Edit an empty file with vim, then try an paste in the following text:
!## NETSCAPE
      Netscape*drawingArea.translations:  #replace    \
      <Btn1Down>:           ArmLink()   \n\
      <Btn2Down>:           ArmLink()   \n\
      ~Shift<Btn1Up>:       ActivateLink()  \n\
      ~Shift<Btn2Up>:       ActivateLink(new-window)  \
      DisarmLink()    \n\
      Shift<Btn1Up>:        ActivateLink(save-only)  \

And it ends up looking like:
!## NETSCAPE
      Netscape*drawingArea.translations:  #replace    \
            <Btn1Down>:           ArmLink()   \n\
                  <Btn2Down>:           ArmLink()   \n\
                        ~Shift<Btn1Up>:       ActivateLink()  \n\
                              ~Shift<Btn2Up>:
ActivateLink(new-window)  \
                                    DisarmLink()    \n\
                                          Shift<Btn1Up>:
ActivateLink(save-only)  \

How do you stop this from happening?