Consider allowing leading underscores in directory names

[igorwwwwwwwwwwwwwwwwwwww]

I recently ran into a case of a package that would install fine via go get having unexpected behaviour when installing via gvt fetch. It turned out that the package I was trying to install had a directory starting with _ which gvt removes as per this logic.

This was rather unexpected, especially considering go get does not have an issue with it. I have opened a ticket with the project in question openzipkin-contrib/zipkin-go-opentracing#42 but also wanted to inquire if gvt should be a bit more permissive in this case -- as it is rather likely that other packages will have the same issue.

Regards,
Igor

[igorwwwwwwwwwwwwwwwwwwww]

Quoting @basvanbeek in the ticket linked above:

As all the code under _thrift is generated I specifically prefixed with _ so it would not be included in tests, coverage, linting, etc.

Seems GVT includes omitting behavior to extend to pulling in code too which is rather strange as one would expect the VC to not include items that should be ignored.

If you agree, perhaps gvt could be more permissive in which files it removes?

[Lyoness]

Bump. 🌷 @FiloSottile

[hiroshi]

Hi,
I forked a patch version to address this issue.
See #91