julia.withPackages: init on supported Julias (1.6, 1.8, 1.9)

Be able to build arbitrary Julia environments in Nixpkgs, in the same style as python.withPackages.

pkgs/development/julia-modules/python/util.py

@@ -0,0 +1,12 @@
+
+import os
+import subprocess
+import tempfile
+
+def get_commit_info(repo):
+  with tempfile.TemporaryDirectory() as home_dir:
+    env_with_home = os.environ.copy()
+    env_with_home["HOME"] = home_dir
+    subprocess.check_output(["git", "config", "--global", "--add", "safe.directory", repo], env=env_with_home)
+    lines = subprocess.check_output(["git", "log", "--pretty=raw"], cwd=repo, env=env_with_home).decode().split("\n")
+    return dict([x.split() for x in lines if len(x.split()) == 2])