Drop jenkins-debian-glue-repoenv package + add dependency on "reprepro | freight" to jenkins-debian-glue

reprepro should be present on every system to avoid failures with
package inclusion in repository. Depending on reprepro in the
main jenkins-debian-glue package avoids that problem while still
supporting setups where cowbuilder etc aren't necessary on
repository-only systems.

Closes: #76
Add jenkins-debian-glue-buildenv-git to Recommends
Release new version 0.7.1