Make rvm requirements do some more work

[jean]

Instead of just printing /usr/bin/apt-get install build-essential ..., execute dpkg -s ... for all the requirements first, and only print the missing ones.

This also allows to check whether the requirements are at the proper version.

[ghost]

@jean You know, feel free to submit patches and pulls instead of just "Don't do this or that" when you're the only one that has an issue with it.

[jean]

As can be seen in the issues I referenced, I'm not the only one.

Even if the issue had not come up before, that would not mean I'm the only one who noticed it. Other people did not take the time and effort to log it so that it may be addressed in future.

When I have the time and expertise required, I do submit pulls. I'm not logging issues for YOU to do, I'm logging them for WHOEVER to do who has the time and need. Including future me.

Issue tracker labels like "feature" and "support" help to filter reports.

[mpapis]

@jean it is planned as part of #512 for RVM2, we limit work on RVM1 to fixes, new features are introduced only by contribution of it's necessary, so #777 will be covered by fixing and #512 is scheduled for RVM2 - unless someone steps in and provides pull request with good quality code.

[mpapis]

reopening as for 1.18 so we can do rvm requirements run or something that just does stupid run of few commands with no validation of dependencies.

[mpapis]

ok this is deprecated by #1431