Adjust php version check to pass the error message the version number (Fixes #617187).
The current version check uses a hard-coded string in the error message. If the php version requirements for Mahara change in the future, then all languages packs will have to be updated. Rather than doing this every time, we can pass the required version to get_string to substitute in instead. Signed-off-by: Andrew Robert Nicols <email@example.com>