Use absolute path in tests
Guard against path traversal and leading '|'

This change adds some checks against path traversal ('..') and
accidentally shelling out (opening a file starting with '|').
Add tests for path traversal errors
Update History.txt
Merge branch 'path_fixes' into 'master'

Path fixes

Improve the path handling in Grit to guard against path traversal and accidentally shelling out.

See merge request !8
Bump VERSION to 2.7.3