python runtime support, fixes heroku-python#8

bin/steps/conda_compile

@@ -1,9 +1,22 @@
+# determine Python version
+DEFAULT_PYTHON_VERSION="python-2.7.9"
+# If no runtime given, assume default version.
+if [ ! -f runtime.txt ]; then
+   echo $DEFAULT_PYTHON_VERSION > runtime.txt
+fi
+PYTHON_VERSION=$(cat runtime.txt)
+# split on '-' and take just the number
+PYTHON_VERSION_NUMBER=`echo $PYTHON_VERSION | cut -d \- -f 2`
+
 if [ ! -d /app/.heroku/miniconda ]; then
     puts-step "Preparing Python/Miniconda Environment (3.5.2)"
     curl -Os http://repo.continuum.io/miniconda/Miniconda-3.7.3-Linux-x86_64.sh
     bash Miniconda-3.7.3-Linux-x86_64.sh  -p /app/.heroku/miniconda/ -b | indent
     rm -fr Miniconda-3.7.3-Linux-x86_64.sh
 
+    conda create -n condaenv python=$PYTHON_VERSION_NUMBER anaconda
+    activate condaenv
+
     conda install pip --yes | indent
 fi