Question: I am an editor for a trade publication with 40 years of experience in journalism. The company wants me to take a job on the events side, writing content, helping with organization, moderating panels, archiving video. They haven’t called it a promotion but it would clearly be more intense work and involve traveling to conferences every other month. I’d like to accept the offer but I want to negotiate a salary increase after a six-month review. Can I do that upfront or do I wait the six months and in either case, what kind of percentage would be equitable?

Answer: 
Since you are using a versioning system: Fix one bug in his code and check the fix into the versioning system. Then fix another bug and check the fix into the versioning system. And so on. So when you need evidence you point your boss to the versioning system, which contains your name 99 times and his name once.

(In a professional environment with experienced developers you use a source code control system in a different way).

And consider that many companies use an internship as a very, very long interview. If that is the case in your company, then by the sounds of it you are passing the interview, and your colleague is not.
* Inform you manager about the Verbatim copies of code from the Internet, and tell that you see a potential legal liability there
* Explicitly state in commit messages which of his commits you fixed
* Your manager listened to you once, so the next time a huge and messy commit comes which breaks something working and could have been caught by the test, you write an email to your coworker with the manager in CC stating that you need he should show you on his machine how he tested the code and how it works.
* When he submitted something which breaks and leaves during the office hours, you go to the manager shortly after he left and ask him to locate your coworker, stating that you would prefer if the coworker helps integrating the code - state that you can do it alone, but it may take more time and state which of your tasks is delayed by this.
* In case this continues, take notes over one week how much work integrating your coworkers mess has caused you, with specific incidents, go to your manager and state that you "can handle it without him"