Using a fake (malloc) RArray is not friendly for the garbage
collector. Fake RArray does not have a heap page, so it causes Variable
Width Allocation to crash when we try to implement it on Arrays.
This commit changes feature_index from a RArray to a darray.
* Tie lifetime of uJIT blocks to iseqs
Blocks weren't being freed when iseqs are collected.
* Add rb_dary. Use it for method dependency table
* Keep track of blocks per iseq
Remove global version_tbl
* Block version bookkeeping fix
* dary -> darray
* free ujit_blocks
* comment about size of ujit_blocks