title: Heroku RPy RHOME discovery
body: <p>I am trying to run a multipack Heroku app that uses Python and R.  I have the multi buildpack installing R first, but RPy's installation is not able to find R despite my modifications to $PATH.  What is going on here?  R sees RHOME as "/app/vendor/R/lib64/R" when init.r runs.</p>
  
  <pre><code>-----&gt; Fetching custom git buildpack... done
  -----&gt; Multipack app detected
  =====&gt; Downloading Buildpack: https://github.com/virtualstaticvoid/heroku-buildpack-r
  =====&gt; Detected Framework: R
     Vendoring R 2.15.1
     Downloading and unpacking R binaries
     Executing init.r script
  [1] "/app/vendor/R/lib64/R" #This is me dumping out RHOME from init.r
     R 2.15.1 successfully installed
  =====&gt; Downloading Buildpack: https://github.com/heroku/heroku-buildpack-python
  =====&gt; Detected Framework: Python
  -----&gt; No runtime.txt provided; assuming python-2.7.4.
  -----&gt; Using Python runtime (python-2.7.4)
  -----&gt; Installing dependencies using Pip (1.3.1)
     Downloading/unpacking rpy2==2.3.5 (from -r requirements/base.txt (line 22))
       Running setup.py egg_info for package rpy2
  
         sh: R: not found
         Error: Tried to guess R's HOME but no R command in the PATH.
         Complete output from command python setup.py egg_info:
         running egg_info
  
     creating pip-egg-info/rpy2.egg-info
  
     writing pip-egg-info/rpy2.egg-info/PKG-INFO
  
     writing top-level names to pip-egg-info/rpy2.egg-info/top_level.txt
  
     writing dependency_links to pip-egg-info/rpy2.egg-info/dependency_links.txt
  
     writing manifest file 'pip-egg-info/rpy2.egg-info/SOURCES.txt'
  
     warning: manifest_maker: standard file '-c' not found
  
  
  
     sh: R: not found
  
     Error: Tried to guess R's HOME but no R command in the PATH.
  
     ----------------------------------------
     Command python setup.py egg_info failed with error code 1 in /tmp/pip-build-u32629/rpy2
     Storing complete log in /app/.pip/pip.log
   !     Heroku push rejected, failed to compile Multipack app
  
  To git@heroku.com:D.git
   ! [remote rejected] master -&gt; master (pre-receive hook declined)
  
  (venvddd)ben@Watt:~/Projects/D/D$ heroku config:get PATH /home/ben/Projects/D/venvddd/bin:/usr/local/heroku/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/app/vendor/R/lib64/R:/app/vendor/R/lib64/R/bin
  </code></pre>