duplicate public_name field leads to poor error message

[agarwal]

If you have two jbuild files with (name mylib), you get a nice error message:

Library "mylib" is defined twice:
- mylib/a/jbuild:3
- mylib/b/jbuild:3
make: *** [dev] Error 1

However, if you mistakenly have the same public_name in multiple jbuild files, you get the following unhelpful error:

Error: exception Invalid_argument("Map.of_list_exn")
Backtrace:
Raised at file "pervasives.ml", line 33, characters 20-45
Called from file "src/scope.ml", line 74, characters 8-204
Called from file "src/super_context.ml", line 89, characters 4-103
Called from file "src/gen_rules.ml", line 1205, characters 6-204
Called from file "src/fiber/fiber.ml", line 359, characters 6-13
make: *** [dev] Error 1

[ghost]

It should be fixed now. Thanks for the report.