Spoofax/928: allows users to choose their own JVM options.

[ghost]

This pull requests allows users to choose their own JVM options:

• ESV support, e.g.: jvm opts: -server -Xss8m -Xmx1024m (Format: -X[ss|mx]<size>[g|G|m|M|k|K])
• At runtime, it takes all the languages in the registry into account to calculate the highest Xss and the highest Xmx. If the highest Xss/Xmx is higher than the current Xss/Xmx, a configuration warning is generated.
• If a plugin specifies no JVM options, then the default options for Spoofax are used (-server -Xss8m -Xmx1024m)
• If there is only one language in the registry, the configuration warning is now named YourLang configuration warning instead of Spoofax configuration warning.

Note: Only -server, Xss and Xmx JVM options are currently supported.

[Gohla]

1. Are you sure that all languages are registered before checkJVMOptions is called?
2. Did you test this by doing a full build of Spoofax using the spoofax-releng repository?

[ghost]

1. Yes, I looked at IMP's code LanguageRegistry.getLanguages() actually makes sure that the LanguageRegistry is initialized. It even works for dynamically loaded languages, which means that you can test the feature by building the project and restarting Eclipse.
2. Yes.

[Gohla]

Thanks!