Implement name_pending RPC call.

Add a new RPC call "name_pending" that lists all pending name operations
in the memory pool together with some decoded information (operation
performed and value the name is set to).
Add getchains RPC command.

Implement a new "getchains" RPC command, that returns all heads of
blockchain forks known.
Add branch info to getchains.

Add additional result fields to getchains output that show the branches
connecting the heads to the main chain.
Use best height in DecodeNameTx.
Update changelog.md
Add missing STL headers.
Merge pull request #2 from phelixbtc/patch-6

Update changelog.md
Merge pull request #79 from domob1812/new-commands

name_pending and getchains RPC commands
Remove unused preqScript argument to SignSignature.

Remove an unused optional argument to the SignSignature functions to
simplify them.
Simplify SignSignature functions.

Simplify the two SignSignature functions by making one call the other
instead of duplicating the code.
Make argument const that can be.

Make a passed-by-ref argument that is never changed const to make this
explicit.
Unify signing of name and non-name inputs.

Unify the signing of name and non-name inputs in the code.  This also
makes signrawtransaction work for name-operation transactions.
Correctly set tx version in createrawtransaction.

If createrawtransaction is called with a name operation, correctly set
its nVersion as a namecoin tx.