0. Introduction of the static:
      TProof::Mgr(const char *url)
   to get the manager to the cluster; this gives access to all the manager
   functionality, included Reset(). TProof::Reset() is removed.

1. Two new classes: TProofLog and TProofLogElem.
   TProofLog contains a list of TProofLogElem, one per node. TProofLogElem
   basically contains a TMacro plus methods to play  with it.

2. The TProofLog object can be retrieved via the manager:

      TProofLog *pl = TProof::Mgr("cluster")->GetSessionLogs()

   by default the last session is retrieved: the signature for GetSessionLogs is

      TProofLog *TProofMgr::GetSessionLogs(Int_t ridx, const char *stag)

   the first argument is a reversed relative index (-1 gets the next to last
   session), the second is the session unique tag; if the second is
   specified the first is ignored.

3. TProofMgr has a new method ReadBuffer to quickly read a buffer from
   a file via XrdProofd: this allows to avoid the second xrootd on the
   redirector and in general is useful when a quick reading is needed.
   Also, the buffer is always retrieved via the master, so we should not
   have firewall problems in accessing directly the xrootd of the workers.

4. In the sandbox I have kept the .sessions file with the active sessions
   and I have added .terminated in each session working dir which have
   been terminated. On the master, each session working dir has the file
   .workers with the relevant information about the workers.

5. The max number of old session workdirs is set to 10 by default
   (configurable in xpd.cf): the sandbox is trimmed when closing a session.

6. Some unrelated changes/fixes contained in the patch:
   - in XrdProofdProtocol:
      - use of /proc (linux, solaris) or sysctl (mac) to verify/search
        for running of a process. For other platforms I have left the
        parsing of the output of 'ps'.
      - I have introduced a 'cron'  thread: it runs every minute and for
        the moment it just cleans a vector; this is the place where to do
        client independent actions, like checking if the config files have
        changed, for example.
      - I have added the possibility to control which user can access
        the cluster; requested by Jan Fiete.

7. The patch contains also several fixes here and there I have found by
   testing.


git-svn-id: http://root.cern.ch/svn/root/trunk@17035 27541ba8-7e3a-0410-8455-c3a389f83636