Fix code and tests on windows.

[sgotti]

Given that I absolutely don't care about windows, this fixes code and tests on it.

PR #21 tried to set the PATH env var in an unix like way with the effect of disabling the go test execution.

This patch:

• Fixes PATH env to add $GOPATH/bin
• Fixes isParentDirectory
• Fixes TestGetLastVendorPath and TestIsParentDirectory
• Handles missing error check on glide list execution

/cc @Fugiman

[FugiTech]

Oops, sorry about that. LGTM!

[sgotti]

@Fugiman Thanks and don't worry. It's a mess handling different path separators between package paths and os paths. Merging.