fix reload_module ignoring pack environment

reload_module loaded the new module code with the global environment,
while require runs modules in their pack environment. After reload,
PACK_ID and other pack globals were nil in the module.

dev/tests/reload_module.lua

@@ -0,0 +1,33 @@
+-- reload_module must run the module in its pack environment, as require does
+local util = require "core:tests_util"
+util.create_demo_world()
+
+-- a pack with a module that uses pack environment (PACK_ID)
+local PACK = "world:content/reload_test"
+file.mkdirs(PACK .. "/modules")
+file.write(PACK .. "/package.json", json.tostring({id="reload_test", title="reload_test"}))
+
+local function write_module(version)
+    file.write(PACK .. "/modules/mod.lua", string.format([[
+local this = {}
+function this.info() return PACK_ID, %d end
+return this
+]], version))
+end
+
+write_module(1)
+app.reconfig_packs({"reload_test"}, {})
+app.tick()
+
+local mod = require "reload_test:mod"
+local packid, version = mod.info()
+assert(packid == "reload_test" and version == 1)
+
+write_module(2)
+reload_module("reload_test:mod")
+packid, version = mod.info()
+assert(version == 2, "module is not reloaded")
+assert(packid == "reload_test", "reloaded module has no pack environment")
+
+app.close_world(true)
+app.delete_world("demo")