use lmodern since the -- are nicer

Fix : if the session points to an edited file that doesn't exist do as if the proof attempt is not edited

print all the edited files which appear in the session.

In conjonction with --print0 which prints '\000' instead of '\n' that
give a safe way to "git add" all the edited files of a session:

why3session info --edited-files --print0 vstte12_bfs.mlw |xargs -0 git add

Since why3session accept the why3session.xml (it uses the basename as
 session directory) you can add all the edited file of all the session
saved in a git repository with:

git ls-files -z |grep -z -e "why3session.xml$" |xargs -0 why3session info --edited-files --print0 | xargs -0 git add

appears only if it is big enough (that give a strange behaviour ;) )

use debug flag

? not verified (or not valid for proof_attempt)
! InternalFailure
O obsolete
A archived

have too complicated semantics. why3session should do the job.

Revert "Why3 replayer: add option remove_converted"

This reverts commit f188489a.

Revert "replay remove converted external proof"

This reverts commit c2887483.

Conflicts:

	src/session/session_tools.ml

It's goal is to allow to view and modify sessions.

Currently three sub-commands :
info : can give the provers used, pretty-print in ascii a session,
     can give the corresponding directory
mod : allow to set obsolete, or modify the archive state of proof attempt
    which corresponds to selected provers
copy : copy a proof attempt by modifing its prover