fixed ticket #435: improving error message on empty session id
bugfix: prevent vishnu sessions pid files corruption

add a file lock to disable concurrent accesses to ~/.vishun/sessions/<pid> file
fixes #135
bugfix: add exception handling code to vishnu session pid files save

Cf. previous commit, in some cases (rare ?), file locking code throws an exception.
First version of pinger, has local path and cout to remove
Now 2 binaries, a pinger and an all pinger that ping all registers elements in dispatcher
Now API services for pings, no python/java yet
Display version good now when ping
Now can ping dispatcher
Fix for compilation on some machines
Handling of CLI
ping make all and nothing
Fix for dispatcher config file
ping Work better with nothing in dispatcher, display sed name with uri
Some cleaning, fix to work when dispatcher has init file
Add a get version service, ping being an extension of it
Rename api function to getServerVersion
Change a new method to list servers in dispatcher
Handling comm_api functions in python
Add a first automtest, fix bug in error detecting when dispatcher down to ping
Add tests and fix a missing return statement