Backed out changeset cfa477946181824f4c769580ebf59710090ba08a Only printenv was changed, not the actual execution of hooks. And not setting an empty value might cause problems on platforms which can't always remove variables from the environment.

adding a
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
a renamed from b:9a263dd772e0159ddfa70fb8a448bb6c7ec8c69f
% test with --rev
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3