Improve error handling when constructing incomplete cycles
Test constructing loops / cycles (100% coverage)
Merge remote-tracking branch 'origin/master' into walk
Add new Walk behavior to CHANGELOG
Merge pull request #87 from clue/walk

Improve constructing Walks (loops and invalid ones)
Merge branch 'master' into remove-graph-getvertexfirst

Conflicts:
	lib/Fhaculty/Graph/Walk.php
	tests/Fhaculty/Graph/WalkTest.php