Add field `allocf_ud` to replace current `ud`.
Since some use it as `mrb_state` associated user data.
add Module#module_function
Fix memory leak for test driver
Merge pull request #2488 from ksss/leak-test

Fix memory leak for test driver
Silence "unused parameter" warnings in C++

This has been done already, but the fixes were accidentally
removed in 249f05e7d70761823ef07a990276f9200e8b3302.
Merge pull request #2489 from Ancurio/silence_cpp_warn

Silence "unused parameter" warnings in C++
Merge pull request #2477 from take-cheeze/allocf_ud

Add field `allocf_ud` to replace current `ud`.
Merge pull request #2478 from dreamedge/add_module_function

add Module#module_function
Refactor sym_equal() in symbol.c
Merge pull request #2490 from suzukaze/refactor_symbol

Refactor sym_equal() in symbol.c