Added a test for the mirror directory name end with at least one slash in cache path

On the official Cygwin setup append a slash when the given mirror does not end
with a slash to the mirror directory.
Fixed the mirror directory name end with at least one slash in cache path
bug #75 Fixed the mirror directory name end with at least one slash in cache path (alquerci)

This PR was merged into the 1.1-dev branch.

Discussion
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| Q               | A
| --------------- | ---
| Bug fix?        | yes
| New feature?    | no
| BC breaks?      | no
| Deprecations?   | no
| Tests pass?     | yes
| Related tickets |
| License         | GNU GPLv3

Commits
-------

7278556 Fixed the mirror directory name end with at least one slash in cache path
dccc46b Added a test for the mirror directory name end with at least one slash in cache path