Some tests used a fake vendor directory placed inside _fixtures to
import some support packages.
In go.mod mode vendor directory are only supported on the root of the
project, which breaks some of our tests.
Since vendor directories outside the root of the project are so rare
anyway it's possible that a future version of go will stop supporting
it even in GOPATH mode.
Also it was weird and unnecessary in the first place anyawy.
If the application being debugged imports two packages with the same
name (but different paths) there was no way to disambiguate the two,
since the character '/' can not appear inside a go identifier.
By allowing users to use a string literal as the package name a package
path can be specified.
Generate names of the concrete types stored inside interface variables
by fully parsing their runtime._type instead of simply using the str
field.
This allows delve to read the contents of an interface variable when
the program imports multiple packages that have the same name. It also
allows delve to correctly interpret some complex anonymous types.
Fixes#455
