Improve error reporting

When creating a new Byteman helper class I had for whatever reason use "final" for my class:

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public final class MyHelper extends Helper {
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When using bmcheck to check the related rules using this class I got this error:

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Compiler.createHelperAdapter : exception creating compiled helper adapter for ...
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This made it pretty hard to find out what's wrong, I added some debug output printing in the method printing this which then gave me the needed clue:

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java.lang.VerifyError: Cannot inherit from final class
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So I'm suggesting to add a bit more helpful exception message at least into this particular method but perhaps also check are there similar methods nearby (which I'm unaware of) that might benefit from similar treatment. Thanks.