The current --server syntax allows for binding to interface or
address. However, in some (admittedly special) cases it is useful to
be able to specify both. This commit introduces the following syntax
to support binding to both interface and address:

--server X.X.X.X@IP@interface#port

Based on my tests, the syntax is backwards compatible with the current
@IP/interface#port. The code will fail if two interface names are given.

v1->v2:
* Add man page description of the extended server syntax (thanks Simon Kelley)
Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>