scripts/controllib.pl: add comment with description of global variables

scripts/controllib.pl: add comment with description of global variables
scripts/dpkg-genchanges.pl:
+ add comment with description of global variables
+ Change Format number to 1.7
+ `Maintainer' is now the actual maintainer as listed in control
+ add `Changed-By' field with maintainer as listed in changelog. Add -e
  flag to override this value
scripts/dpkg-buildpackage.sh: pass -e on to dpkg-genchanges
scripts/dpkg-source.1: document new -e option, update copyright