Split up script into a core and utility part. #4344

Currently script.{h,cpp} defines both a core data structure (CScript, and its associated opcodes) with serializations, and several sets of utlity code related to it (signing, verification, identification).

I believe these should be separated, so with all the modularlization efforts, the core data structures can go in a common library that does not pull in keystore, for example (which pulls in key, crypto code, ...).

Related, the abstract CKeyStore class should probably move to the new place where signing ends up, while the implementations can stay in keystore. This breaks the cyclic dependency between keystore and script.

I spent some time on this last week. I managed to sever a few dependencies, but I was afraid that it would be hard to convince the others that this was worth doing. Good to see that it's on your radar as well.

I'll publish my work in a branch next week. Problem is, there will likely need to be a good bit of intermediary reorg with seemingly no benefit before the real splits can happen.

I tend to lump things into three buckets: CScript class, script eval, everything else.

Seems like it would not require lots of reorg to attain something like that as a first step.

@jgarzik SGTM

In case someone missed it, #4754 does basically what is said here and #4755 goes a little bit beyond that separating "everything else" into script/sign, script/standard, script/compressor and wallet/ismine.

@sipa I think this can be closed now, no?