fix logg() in compile, add more logging to engine.rb when the problem cannot be found
handle the case when problem id or submission id is null. Grader will simply skip such request. Add more report on console (for command line grading)
(mercurial grafted from d233105d3965c5368c9b33125f390e39b25f910e)

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extra : source : d233105d3965c5368c9b33125f390e39b25f910e
Merge pull request #3 from nattee/master

Quick fix for grader crash problem