Always pass basename to install_p

Currently, when called with one argument, dst is set to self, i.e. the
directory into which the source file should be moved.

When called with a second argument (for renames), dst is the full path,
including the basename, to the moved file.

Instead, let's always pass the full path, which means we can remove the
branching logic around computing dst.

Library/Homebrew/extend/pathname.rb

@@ -21,28 +21,23 @@ class Pathname
           opoo "tried to install empty array to #{self}"
           return
         end
-        src.each {|s| install_p(s) }
+        src.each { |s| install_p(s, File.basename(s)) }
       when Hash
         if src.empty?
           opoo "tried to install empty hash to #{self}"
           return
         end
-        src.each {|s, new_basename| install_p(s, new_basename) }
+        src.each { |s, new_basename| install_p(s, new_basename) }
       else
-        install_p(src)
+        install_p(src, File.basename(src))
       end
     end
   end
 
-  def install_p src, new_basename = nil
+  def install_p(src, new_basename)
     raise Errno::ENOENT, src.to_s unless File.symlink?(src) || File.exist?(src)
 
-    if new_basename
-      new_basename = File.basename(new_basename) # rationale: see Pathname.+
-      dst = self+new_basename
-    else
-      dst = self
-    end
+    dst = join(new_basename)
 
     src = src.to_s
     dst = dst.to_s

Library/Homebrew/install_renamed.rb

@@ -1,8 +1,6 @@
 module InstallRenamed
-  def install_p _, new_basename = nil
+  def install_p(_, new_basename)
     super do |src, dst|
-      dst += "/#{File.basename(src)}" if File.directory? dst
-
       if File.directory? src
         Pathname.new(dst).install Dir["#{src}/*"]
         next