Bug#707771: symbol rename in libapt-pkg4.12

[GUO Yixuan <culu.gyx@gmail.com>]

Hi,

I think this is the reason: apt is at 0.9.7.8, but libapt-pkg4.12 is
0.9.8, and the following rename, introduced in 0.9.7.9~exp2.

   * apt-pkg/indexcopy.cc:
     - rename RunGPGV to ExecGPGV and move it to apt-pkg/contrib/gpgv.cc
   * apt-pkg/contrib/gpgv.cc:
     - ExecGPGV is a method which should never return, so mark it as such
       and fix the inconsistency of returning in error cases
     - don't close stdout/stderr if it is also the statusfd
     - if ExecGPGV deals with a clear-signed file it will split this file
       into data and signatures, pass it to gpgv for verification
     - add method to open (maybe) clearsigned files transparently

Cheers,

GUO Yixuan