Force analysis of named paths in glide get

[sdboyer]

This addresses the issue where glide get fails to incorporate transitive dependencies of deps named on the command line and not already imported in the project.

Fixes #690 I think; related to #468

[nsilberman]

hi @sdboyer , works well on Mac, not on TravisCI (docker instance on ubuntu 12) while executing glide up --all-dependencies

[INFO]  --> Fetching updates for github.com/andybalholm/cascadia.
[ERROR] Could not find /home/travis/.glide/cache/src/https-golang.org-x-sys/unix: open /home/travis/.glide/cache/src/https--home-travis-.glide-cache-src-https-golang.org-x-sys-unix: no such file or directory
[ERROR] Dependency golang.org/x/sys/unix (/home/travis/.glide/cache/src/https-golang.org-x-sys/unix) failed to resolve: open /home/travis/.glide/cache/src/https--home-travis-.glide-cache-src-https-golang.org-x-sys-unix: no such file or directory.
[ERROR] Failed to retrieve a list of dependencies: open /home/travis/.glide/cache/src/https--home-travis-.glide-cache-src-https-golang.org-x-sys-unix: no such file or directory

[sdboyer]

@nsilberman that's the other half of the issue that got conflated in with #468, i think - note the double-nested path within the cache directory. i think i aim to deal with that one separately