CodeAnalysis props are dropped on conversion

[ryandle]

We converted some projects using --keep-current-tfms. It completes successfully without warning, but we noticed that the following props were quietly dropped / not included in the new sdk-style project. I would have expected at least a warning that these couldn't be converted.

<CodeAnalysisRuleSet>..\..\build\fxcop.ruleset</CodeAnalysisRuleSet>
<CodeAnalysisIgnoreGeneratedCode>true</CodeAnalysisIgnoreGeneratedCode>
<TreatWarningsAsErrors>true</TreatWarningsAsErrors>

[jmarolf]

This looks like a bug. we shouldn't remove ruleset items