Force unlock message in Windows shows \ instead of / in the path

[billdenney]

In this line:

drake/R/decorate_storr.R

Line 235 in c02f19e

.self$path,

The error message is shown with backslashes () instead of forward slashes (/) in Windows, so it cannot be simply pasted.

The message looks like:

drake::drake_cache("C:\some_path\.drake")$unlock()

When it should look like:

drake::drake_cache("C:/some_path/.drake")$unlock()

Using normalizePath() should make it work as desired. (PR coming shortly.)

[wlandau]

Both should work even on Windows, but the second version is clearer.

[billdenney]

The first message gave an error like:

"\." is not a recognized escape sequence.

Thanks for merging!