Stop joining symbols to pathnames

Ruby 2.2's native Pathname#/ accepts only string-like objects.

Library/Homebrew/build.rb

@@ -117,7 +117,7 @@ class Build
     ENV.activate_extensions!
 
     deps.map(&:to_formula).each do |dep|
-      opt = HOMEBREW_PREFIX/:opt/dep
+      opt = HOMEBREW_PREFIX.join("opt", dep.name)
       fixopt(dep) unless opt.directory?
     end
 

Library/Homebrew/cmd/uninstall.rb

@@ -36,7 +36,7 @@ module Homebrew extend self
   end
 
   def rm_opt_link name
-    optlink = HOMEBREW_PREFIX/:opt/name
+    optlink = HOMEBREW_PREFIX.join("opt", name)
     optlink.unlink if optlink.symlink?
   end
 

Library/Homebrew/extend/pathname.rb

@@ -321,7 +321,7 @@ class Pathname
   end
 
   def find_formula
-    [self/:Formula, self/:HomebrewFormula, self].each do |d|
+    [join("Formula"), join("HomebrewFormula"), self].each do |d|
       if d.exist?
         d.children.each do |pn|
           yield pn if pn.extname == ".rb"

Library/Homebrew/keg.rb

@@ -248,7 +248,7 @@ class Keg < Pathname
   end
 
   def optlink
-    from = HOMEBREW_PREFIX/:opt/fname
+    from = HOMEBREW_PREFIX.join("opt", fname)
     if from.symlink?
       from.delete
     elsif from.directory?