libbitcoinscript

This does the minimal effort to generate a libbitcoinscript.so which can VerifyScript, though nothing else is exposed.

Build with ./configure --enable-shared=yes and you'll find a libbitcoinscript.so installed (or in src/.libs).

It weighs quite a bit, but it works, so I think its worth merging and then trimming down (and adding features) as we go (Ive already got one or two others ready, but first things first).

Please do not ACK this unless you've verified there are no changes before/after the copy/paste.
If VerifyScript becomes a templated function as shown in https://github.com/jtimon/bitcoin/commit/886260173ee9367b5c00d445fa8f7b678921da4e (well, something simpler and less dirty, that's just a thinking branch for now), the standalone can instantiate the functions with its own minimal CTransaction type without any need to link core.o or include core.h
Maybe other C++ implementations like libcoin or libbitcoin decide to consume this templated version directly instead of the C API, also with their own Transaction classes.