Change algorithm to generate id, if create an already existing id, append a number at the end
Move define_identifier from IMS to UMS
Update model with data changes
Update tests for UMS and updated documentation for moving define functions
Add new tests with same login generated
Fix xml links
Fix typo
Update asta documents
Fixed cpplint errors
Updated Design.asta and associated docs
Update images
Add missing manpages
Set version to 3.1.1
Regenerate all documentation for release 3.1.1
Update changelog
bugfix: prevent vishnu sessions pid files corruption

add a file lock to disable concurrent accesses to ~/.vishun/sessions/<pid> file
fixes #135