Make -0 option fake success of lsetxattr(2) and fsetxattr(2).

This is required to install packages on Tizen (SMACK mechanism).

Signed-off-by: Rémi Duraffort <remi.duraffort@st.com>
Make PRoot manual and command-line-interface agree on -S.
Fix ELF auxiliary vectors to make GDB DSO support work under PRoot.

ELF auxiliary vectors have to be fixed because some of them are set to
unexpected values when the ELF interpreter is used as a loader
(AT_BASE for instance).  So far, this issue bugs GDB only.
Make "kompat" extension (-k option) use the new ELF auxiliary vector interface.

This simplifies the code a bit and it has exposed a bug in the ELF
auxiliary vector interface.
Make -i/-0 options override AT_*ID ELF auxiliary vectors.

Ref: https://github.com/cedric-vincent/PRoot/issues/56