X11Requirement: Inherit from generic class [macOS]

[sjackman]

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Fix the warning: already initialized constant X11Requirement
See #3483 (comment)

[sjackman]

Pushed too soon. Give me a sec…

[sjackman]

The macOS version of X11Requirement now inherits from the generic version.
I modified Requirement::satisfy to permit redefining @satisfied in the derived class.
Requirement::satisfy is called in three modes.

1. With no arguments as a predicate by satisfied?.
2. With a block, e.g. satisfy { which "foo" }
3. With a boolean, e.g. satisfy true

[ilovezfs]

❤️

[sjackman]

☺️

[MikeMcQuaid]

👍 once this is 🍏. Thanks for the fast turnaroud here @sjackman. If you can refactor JavaRequirement or OSXFuseRequirement at all to use the approach you've done here that'd be great.

[ilovezfs]

Thanks @sjackman! 🚢'd

[sjackman]

I took a quick look at JavaRequirement and OSXFuseRequirement. I didn't see any obvious code duplication or refactoring made possible by my fix to satisfy.