Use single spacing between sentences

In logintoboggan.module, the error text "Access denied.  You may need to login below or register to access this page." has two spaces between the sentences. This is problematic, as 1) it can be confusing to users trying to use string overrides to change it since the double space is not displayed when the string is displayed in the browser, 2) it's bad form.

In the following patch, I propose removing the space to avoid confusion and make the gods of typography happy.

Thanks for your consideration.