28f8b66 Diagnose unsuitable outputs in lockunspent(). (Eelis)
Pull request description:
Fixes#2667.
This is a simplified version of pull request #3574, which was abandoned by its author.
I added some tests as well.
Tree-SHA512: e63e00dec8b1b232079380183805cb0b0b18c78ea6bea769837949aab984689d7f68b2ccfe66b1873517b040b9e616ce0eb058575c3d4382aa8c26eebcf1f14e