brew reinstall: Is able to work for all formulae

... and not just installed ones. Of course, strictly speaking,
reinstalling not-yet-installed formulae makes semantically little
sense, but the big win is that we can tell people (after we have
resolved an issue) to `brew reinstall <formula>` and even if a user
has removed that formula in the meantime, reinstall will do the right
thing. Basically adding --force to uninstall. I think this makes
reinstall more robust.

Library/Homebrew/cmd/reinstall.rb

@@ -6,6 +6,9 @@ module Homebrew extend self
     # At first save the named formulae and remove them from ARGV
     named = ARGV.named
     ARGV.delete_if { |arg| named.include? arg }
+    # We add --force because then uninstall always succeeds and so reinstall
+    # works for formulae not yet installed.
+    ARGV << "--force"
     clean_ARGV = ARGV.clone
 
     # Add the used_options for each named formula separately so