Prefixes should not allow trailing slashes

[xsawyerx]

In order to be consistent with false routes (issue #581), prefixes should not allow postfix slash.

If:

• Prefixes do not have trailing slash
• All routes must start with slash (indicated at Routes must have leading slash #581)

We could generate paths that are consistent:

• Prefix will always connect to paths with a single /.
• Users who want multiple slashes can add them to the route, and it will work.
• Element of least surprise.

[xsawyerx]

Now that I look at it again, I realize this might be a mistake because /admin should not be the same as /admin/. Also, HTTP protocol dictates that /admin// is different than /admin/, so that means we need to support both, even if the user is making a mistake.