Choice for bug tracking tool probably depends on project requirements. However as well as mantis, I have used bugzilla, Jira, donedone and sifter and even spreadsheets. For all cases, I could write as many scripts as you want to prepare test data, make screenshots or emulate requests from the server etc.
But, I agree - over all Mantis is better bug tracking tool as it has wide device support and compatibility. It works with multiple databases like MySQL, PostgreSQL, MS SQL and integrated applications like chat, time tracking, wiki..
Anyway, the main QA's tool is me. I know Warnings and Optimizations are for a developer to fix, if he/she chooses to fix. In this case I have a good code review practice to have the code generate minimal possible warnings. I was able to resolve many warnings as possible. However, at times, it is possible that XCode generates some stray warnings. I am also capable to fix those. I am so much familiar with comprehensive list of reasons( Apple Appstore Review Guidelines documents) that can lead to your app's rejection in the review process
I always work on a terminology of the below process, although I use different tools, this process still applies to me:
Preconditions. Determine what conditions are mandatory for you to review the change. If any of your conditions are missing, reject the update and reopen the issue.
Read the issue. Make sure you are aware of the full scope of the problem.
-Reproduce the original state on the master branch.