Add pour_bottle? method to Formula.

Allows a formula to selectively disable bottle pouring.
e.g. the default Boost bottle does not work with a brewed Python.

Fixes Homebrew/homebrew#17142

Library/Homebrew/bottles.rb

@@ -15,6 +15,7 @@ def install_bottle? f
     and f.downloader.local_bottle_path
   not ARGV.build_from_source? \
     and MacOS.bottles_supported? \
+    and f.pour_bottle? \
     and f.build.used_options.empty? \
     and bottle_current?(f)
 end

Library/Homebrew/formula.rb

@@ -162,6 +162,13 @@ class Formula
     @downloader.cached_location
   end
 
+  # Can be overridden to selectively disable bottles from formulae.
+  # Defaults to true so overridden version does not have to check if bottles
+  # are supported.
+  def pour_bottle?
+    true
+  end
+
   # tell the user about any caveats regarding this package, return a string
   def caveats; nil end