Taps can only have one directory of formula

Rationale: Let's not have duplicate-names. Insisting on only one directory lets the filesystem enforce this unique-naming criteria for us.

We special-case adamv/alt for now, until we remove it.

Library/Homebrew/extend/pathname.rb

@@ -318,16 +318,33 @@ class Pathname
     system '/usr/bin/install-info', '--delete', '--quiet', self.to_s, (self.dirname+'dir').to_s
   end
 
-  def find_formula pwd = self
+  def all_formula pwd = self
     children.map{ |child| child.relative_path_from(pwd) }.each do |pn|
       yield pn if pn.to_s =~ /.rb$/
     end
     children.each do |child|
-      child.find_formula(pwd) do |pn|
+      child.all_formula(pwd) do |pn|
         yield pn
       end if child.directory?
     end
   end
+
+  def find_formula
+    # remove special casing once tap is established and alt removed
+    if self == HOMEBREW_LIBRARY/"Taps/adamv-alt"
+      all_formula do |file|
+        yield file
+      end
+      return
+    end
+
+    [self/:Formula, self/:HomebrewFormula, self].each do |d|
+      d.children.map{ |child| child.relative_path_from(self) }.each do |pn|
+        yield pn if pn.to_s =~ /.rb$/
+        break
+      end if d.exist?
+    end
+  end
 end
 
 # sets $n and $d so you can observe creation of stuff