SharePoint - How to display stack trace error in the browser.

Here's an oldie, but a goodie!

SharePoint provides "friendly error messages", that are comparable to an inane conversation with a stranger about the weather at the bus stop.
For example:
"An unexpected error has occurred"     (The plot thickens...)

Sometimes you just want to know why you can't browse to a SharePoint page, without having to root through ULS/IIS logs on the server.

To disable these custom error messages:

Now when you navigate to the contentious page you should get a full stack trace and details!