use Module#const_get instead of eval

* may be a problem if the constant is scoped (like A::B), but this is not the case
  (const.split('::').inject(Object) { |c, part| c.const_get part } would solve that)
* this was noticed in a comment of 9afc85a but it has disappeared

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Homebrew/formula.rb

@@ -378,7 +378,7 @@ def self.factory name
 
     begin
       klass_name = self.class_s(name)
-      klass = eval(klass_name)
+      klass = Object.const_get klass_name
     rescue NameError
       # TODO really this text should be encoded into the exception
       # and only shown if the UI deems it correct to show it

bin/brew

@@ -71,10 +71,9 @@ begin
 
   # Add example external commands to PATH before checking.
   ENV['PATH'] += ":#{HOMEBREW_REPOSITORY}/Library/Contributions/examples"
-
   if system "/usr/bin/which -s brew-#{cmd}"
     %w[CACHE CELLAR LIBRARY_PATH PREFIX REPOSITORY].each do |e|
-      ENV["HOMEBREW_#{e}"] = eval "HOMEBREW_#{e}"
+      ENV["HOMEBREW_#{e}"] = Object.const_get "HOMEBREW_#{e}"
     end
     exec "brew-#{cmd}", *ARGV
   elsif require? `/usr/bin/which brew-#{cmd}.rb`