Proc shouldn't have `initialize` method

Implement Kernel.#caller

This issue was reported by https://hackerone.com/ssarong

This issue was reported by https://hackerone.com/icanthack
The solution is suggested by @clayton-shopify.

Fix broken MRB_INT64

Fix 36fc1f14 not checking in the right location

Fix a typo in string.h.

This issue was original reported by https://hackerone.com/icanthack
https://hackerone.com/titanous suggested the solution.
`regs` may be reallocated in the function call.

This issue was reported by https://hackerone.com/tunz

close #3389
This issue was reported by https://hackerone.com/ston3

close #3384
This issue was reported by https://hackerone.com/brakhane

This issue was reported by https://hackerone.com/volc

Put package's libs flag after %{objs}

In case LDFLAG contains "-Wl,--as-needed" or "--as-needed" is enabled by
default, "-l" flags should appear after objs specifiction.

Pass when assert returns a false value

This issue was reported by https://hackerone.com/an0n-j

Check intern object returned by mrb_check_string_type

Update Copyright to 2017

Signed-off-by: Daniel Bovensiepen <daniel@bovensiepen.net>

Removed ununnecessary escape character '\' in libmruby.flags.mak

Rewrite String#prepend with Ruby

This issue was reported by https://hackerone.com/an0n-j

Fix #3357