Bug fixes in query method. [refs #245]
Added tests for exact inference methods and classes [refs #245]
Check for raising error if check_model fails
adds a new ModelError exception
very minor changes
Revert "very minor changes"

This reverts commit 111cd8c4190d1fa0832e6f92a9edeb71f7c74280.
minor changes
Merge pull request #1 from ankurankan/pr/246

Minor changes in PR
Code cleanup in exact inference methods.
Merge pull request #246 from abinashpanda/dev

Query method for VariableElimination.