Check existence of `curses` module before start building PyPy (#244)

plugins/python-build/bin/pyenv-install

@@ -184,22 +184,23 @@ fi
 
 # PyPy requires existing Python 2.x to build
 if [[ "${VERSION_NAME}" == "pypy-"*"-src" ]]; then
-  PYENV_VERSION="$(pyenv-whence "python2.7" 2>/dev/null | tail -n 1 || true)"
-  if [ -n "${PYENV_VERSION}" ]; then
-    export PYENV_VERSION
-  else
-    PYENV_VERSION="$(pyenv-whence "python2.6" 2>/dev/null | tail -n 1 || true)"
-    if [ -n "${PYENV_VERSION}" ]; then
-      export PYENV_VERSION
-    else
-      PYENV_VERSION="$(pyenv-whence "python2.5" 2>/dev/null | tail -n 1 || true)"
-      if [ -n "${PYENV_VERSION}" ]; then
-        export PYENV_VERSION
-      else
-        echo "pyenv-install: $VERSION_NAME requires CPython 2.[567] to build" >^2
-        exit 1
+  if [ -z "$PYENV_RPYTHON_VERSION" ]; then
+    for version in $(pyenv-versions --bare | sort -r); do
+      if [[ "$version" == 2.[567] ]] || [[ "$version" == 2.[567].* ]]; then
+        PYENV_RPYTHON_VERSION="$version"
       fi
+    done
+  fi
+  if [ -n "$PYENV_RPYTHON_VERSION" ]; then
+    if PYENV_VERSION="$PYENV_RPYTHON_VERSION" pyenv-exec python -c 'import curses' 1>/dev/null 2>&1; then
+      export PYENV_VERSION="$PYENV_RPYTHON_VERSION"
+    else
+      echo "pyenv-install: $VERSION_NAME: PyPy requires \`curses' in $PYENV_RPYTHON_VERSION to build from source." >&2
+      exit 1
     fi
+  else
+    echo "pyenv-install: $VERSION_NAME: PyPy requires Python 2.5, 2.6 or 2.7 to build from source." >&2
+    exit 1
   fi
 fi