v50

Merge branch 'save_verbose'

v49

Merge branch 'pr/396'

v48: restore: handle a case of empty GOPATH

When godep restore is executed with empty GOPATH, it fails with error
message like below:
$ godep restore
panic: runtime error: index out of range

goroutine 1 [running]:
main.download(0xc82012a000, 0x0, 0x0)
        /home/mitake/gopath/src/github.com/tools/godep/restore.go:104 +0x1cb8
main.runRestore(0xaffe00, 0xc82000a390, 0x0, 0x0)
        /home/mitake/gopath/src/github.com/tools/godep/restore.go:42 +0x3a5
main.main()
        /home/mitake/gopath/src/github.com/tools/godep/main.go:118 +0xd9f

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
        /usr/local/go/src/runtime/asm_amd64.s:1696 +0x1

This commit lets the command handle such a case with a little bit
grace error message like this:
$ godep restore
godep: Error restore requires GOPATH but it is empty.

v47: Separate case for devel vs go1.6, with same logic as 1.6 check

When go is compiled from source, the major version is 'devel'.
A third conditional has been added to check for this case in order
to enable vendoring when built from source.

v46

Merge branch 'pr/387'

v45

Merge branch 'pr/385'

v44: Clean the root dir

Otherwise a root that ends in / will cause vendor detection to loop
forever.

Fixes #382

v43: Better Godep file handling error message

Fixes #372 (or at least helps inform the user)

v42: Fix a bunch of GO15VENDOREXPERIMENT issues

- Find package directories better. Previously we used build.FindOnly
  which didn't work the way I expected it to (any dir would work w/o
  error).
- Set the VendorExperiment bool based on go version as 1.6 defaults to
  on.
- A bunch of extra debugging for use while sanity checking myself.
- vendor flag for test structs.
- Some tests for vendor/ stuff:
    - Basic Test
    - Transitive
    - Transitive, across GOPATHs + collapse vendor/ directories.

Should Fix #358

v41

Merge branch 'pr/343'