Exclude .git directories and files in them by default

Note that this makes a list of all files in .git directories and is
thus very slow.

Author: brechtm

poetry/core/vcs/git.py

@@ -256,8 +256,9 @@ def get_ignored_files(self, folder=None):  # type: (...) -> list
 
         args += ["ls-files", "--others", "-i", "--exclude-standard"]
         output = self.run(*args)
+        dotgit = list(str(path.relative_to(folder)) for path in folder.rglob(".git/*"))
 
-        return output.strip().split("\n")
+        return dotgit + output.strip().split("\n")
 
     def remote_urls(self, folder=None):  # type: (...) -> dict
         output = self.run(