Use canonical name for VIRTUAL_ENV as a workaround for IPython (fixes #113)

bin/pyenv-sh-activate

@@ -14,6 +14,10 @@
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
 
+resolve_link() {
+  $(type -p greadlink readlink | head -1) "$1"
+}
+
 unset FORCE
 unset QUIET
 unset VERBOSE
@@ -86,6 +90,10 @@ done
 shell="${PYENV_SHELL:-${SHELL##*/}}"
 prefix="$(pyenv-prefix "${venv}")"
 
+if [ -L "${prefix}" ]; then
+  prefix="$(resolve_link "${prefix}" 2>/dev/null)"
+fi
+
 if [[ "${VIRTUAL_ENV}" == "${prefix}" ]]; then
   if [ -z "${QUIET}" ]; then
     echo "pyenv-virtualenv: version \`${venv}' is already activated" 1>&2