This Pull Request fixes/closes #2147.

It will changes the following:

• Disable edit [e] command when not at head revision
• Add open [o] command to open the file if not at head revision
• Add go to head [g] command to jump to that file at head revision (If exist)
• Add proper error messages if tempfile cannot be created or opened ?
• Add proper error messages if go to head failed due to file is not presented ?
• Remove temporary file after close
• Add unittests

I followed the checklist:

• I added unittests
• I ran make check without errors
• I tested the overall application
• I added an appropriate item to the changelog