src: fix process.getuid() return value

And process.getgid() too.

Commit ed80638 changed fs.chown() and fs.fchown() to only accept
unsigned integers. Make process.getuid() and process.getgid() follow
suit.

This commit should unbreak npm on OS X - it's hitting the new 'uid must
be an unsigned int' check when installing as e.g. user 'nobody' (which
has an UID of -2 in /etc/passwd or 4294967294 when cast to an uid_t.)

Fixes #5904.

src/node.cc

@@ -1528,15 +1528,15 @@ static gid_t gid_by_name(Handle<Value> value) {
 
 static Handle<Value> GetUid(const Arguments& args) {
   HandleScope scope;
-  int uid = getuid();
-  return scope.Close(Integer::New(uid));
+  uid_t uid = getuid();
+  return scope.Close(Integer::NewFromUnsigned(uid));
 }
 
 
 static Handle<Value> GetGid(const Arguments& args) {
   HandleScope scope;
-  int gid = getgid();
-  return scope.Close(Integer::New(gid));
+  gid_t gid = getgid();
+  return scope.Close(Integer::NewFromUnsigned(gid));
 }