Updated vendor/oniguruma to 2f0ce672.
Use builtin mechanism in Onigmo for thread safety

This reduces the cases we need lock, since Onigmo does it itself for
cases where needed with the defined headers. From a manual code audit of
Onigmo, it looks like this actually results in not using any locks with
the options we provide for Onigmo.
Revert "Generate global symbol names for primitives"

This reverts commit e9d6f2a728fa5cab31ba95f2f96eaba7c528a555.

This creates very long compile times for shared_state.cpp because of the
large number of globals.
Assign slot accessor direct primitive pointer
Additional test cases on Integer#chr regarding invalid codepoints.

Additional tests have been written to ensure RangeError is raised on
a selection of invalid codepoints from UTF-8 and UTF-16.
Stricter test in String::from_codepoint regarding invalid codepoints.

Checking if ONIGENC_CODE_TO_MBC(...) <= 0 is not enough in discovering
if we're trying to convert an invalid codepoint into a string.
Using Encoding::precise_mbclen ensures the problem is caught and raised.
Merge pull request #2376 from razielgn/feature-improved-integer-chr-encoding-handling

Integer#chr raises RangeError on more invalid codepoints.
increment global serial if included module has constants
add spec for Module#include shadowing constants
Merge pull request #2378 from charliesome/invalidate-method-cache-if-included-module-has-constants

Invalidate method cache if included module has constants