bin/debsources-main: add interpolation support for log_file
bin/debsources-main: add interpolation support for log_file

vivekanand1101/debsources,nonas/debian-qa,oorestisime/debsources,Debian/debsources,zacchiro/debsources,zacchiro/debsources,sophiejjj/debsources,clemux/debsources,clemux/debsources,matthieucan/debsources,oorestisime/debsources,matthieucan/debsources,devoxel/debsources,matthieucan/debsources,zacchiro/debsources,devoxel/debsources,vivekanand1101/debsources,oorestisime/debsources,devoxel/debsources,nonas/debian-qa,Debian/debsources,clemux/debsources,devoxel/debsources,vivekanand1101/debsources,vivekanand1101/debsources,clemux/debsources,clemux/debsources,devoxel/debsources,vivekanand1101/debsources,nonas/debian-qa,Debian/debsources,Debian/debsources,Debian/debsources,zacchiro/debsources,matthieucan/debsources,zacchiro/debsources,sophiejjj/debsources,sophiejjj/debsources,sophiejjj/debsources,oorestisime/debsources,sophiejjj/debsources,nonas/debian-qa,matthieucan/debsources,oorestisime/debsources