Plugin: Fix PM URL creation in shortcodes

This patch fix PM URL creation using shortcodes.

Fix Bug: #502
ref: https://github.com/e107inc/e107/issues/502

Signed-off-by: Ajay Bhargav <bhargav.ajay@gmail.com>
Merge pull request #503 from ajaybhargav/master

Plugin: Fix PM URL creation in shortcodes