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.
I agree with @sipa here. Include files are the interface for the implementation file. Including one but not linking the other is confusing. Please avoid that. Moving functions from the .cpp to the .h should not result in build errors.

I'm sure what you want can be solved some other way. I wouldn't worry about size of the resulting library at all in this initial pull.