Add --bare option to pyenv version

It just points at pyenv version-name.  This adds consistency with the behavior
of `pyenv versions --bare`

libexec/pyenv-version

@@ -1,9 +1,10 @@
 #!/usr/bin/env bash
 # Summary: Show the current Python version(s) and its origin
+# Usage: pyenv version [--bare]
 #
 # Shows the currently selected Python version(s) and how it was
-# selected. To obtain only the version string, use `pyenv
-# version-name'.
+# selected. To obtain only the version string, use `pyenv version
+# --bare` or `pyenv version-name'.
 
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
@@ -13,8 +14,25 @@ OLDIFS="$IFS"
 IFS=: PYENV_VERSION_NAMES=($(pyenv-version-name)) || exitcode=$?
 IFS="$OLDIFS"
 
+unset bare
+for arg; do
+    case "$arg" in
+        --complete )
+            echo --bare
+            exit ;;
+        --bare ) bare=1 ;;
+        * )
+          pyenv-help --usage version >&2
+          exit 1
+          ;;
+    esac
+done
 for PYENV_VERSION_NAME in "${PYENV_VERSION_NAMES[@]}"; do
+  if [[ -n $bare ]]; then
+      echo "$PYENV_VERSION_NAME"
+  else
       echo "$PYENV_VERSION_NAME (set by $(pyenv-version-origin))"
+  fi
 done
 
 exit $exitcode