sysutils/duplicity: Update to 0.7.16

• Enable option PEXPECT as default [1]
• Fix shebang errors [1]
• Update the deprecated way of setting Python version
• Fix WWW

Changes: https://launchpad.net/duplicity/+milestone/0.7.16

Submitted by: mmokhi [1]
Differential Revision: D14052 [1]