use mrb_bool, FALSE and TRUE more

It doesn't matter to me if one is using FALSE/TRUE instead of 1/0
but I prefer a type (alias) which emphasizes boolean vars to int.
I changed 1/0 to FALSE/TRUE anyway.
Store raw stack address in callinfo instead of offset from stbas
Merge pull request #1674 from cremno/mrb_bool-FALSE-TRUE

use mrb_bool, FALSE and TRUE more
Merge branch 'original2' of https://github.com/miura1729/mruby into miura1729-original2
initialize ci->stackent at the top; #1691