Allow group users write to the controlling UNIX-socket.

No visible changes for BSD users, so this is Linux-only
related issue. See this RHBZ for rationale:

https://bugzilla.redhat.com/626863

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Better UNIX-socket access rights policy

Change UNIX-socket's group access rights only if "run as guid" has been
specifically requested. Otherwise that change might constitute mild
security risk for existing deployments, i.e. we are breaking POLA by
introducing ability to use socket to group users, where there has been
none previously.

See Maksym's note no.1:

* https://github.com/sippy/rtpproxy/pull/10#issuecomment-60554402

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Update help output

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Allow overriding UNIX-socket mode

Allow user to explicitly set access mask to the controlling UNIX-socket.
Mode 0755 is the default value.

See Maksym's note no.2:

* https://github.com/sippy/rtpproxy/pull/10#issuecomment-60554402

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Documented V,L,A,w options

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Merge pull request #10 from lemenkov/unix_socket_fix_permissions

o Allow group users write to the controlling UNIX-socket or in general set some custom access mode to the socket;
o Update documentation on V, L and A options.