Fix npm#2597 Don't set GIT_* envs in child processes

lib/cache.js

@@ -386,15 +386,15 @@ function addRemoteGit (u, parsed, name, cb_) {
     var tmp = path.join(npm.tmp, Date.now()+"-"+Math.random())
     mkdir(path.dirname(tmp), function (er) {
       if (er) return cb(er)
-      exec( npm.config.get("git"), ["clone", u, tmp], null, false
+      exec( npm.config.get("git"), ["clone", u, tmp], gitEnv(), false
           , function (er, code, stdout, stderr) {
         stdout = (stdout + "\n" + stderr).trim()
         if (er) {
           log.error("git clone " + u, stdout)
           return cb(er)
         }
         log.verbose("git clone "+u, stdout)
-        exec( npm.config.get("git"), ["checkout", co], null, false, tmp
+        exec( npm.config.get("git"), ["checkout", co], gitEnv(), false, tmp
             , function (er, code, stdout, stderr) {
           stdout = (stdout + "\n" + stderr).trim()
           if (er) {
@@ -410,6 +410,20 @@ function addRemoteGit (u, parsed, name, cb_) {
 }
 
 
+var gitEnv_
+function gitEnv () {
+  // git responds to env vars in some weird ways in post-receive hooks
+  // so don't carry those along.
+  if (gitEnv_) return gitEnv_
+  gitEnv_ = {}
+  for (var k in process.env) {
+    if (k.match(/^GIT/)) continue
+    gitEnv_[k] = process.env[k]
+  }
+  return gitEnv_
+}
+
+
 // only have one request in flight for a given
 // name@blah thing.
 var inFlightNames = {}