Try removing an empy UNIX clause so that the else clause matches UNIX.  This is an attempt to fix #260 with almost no understanding of cmake.
Also install libqethereum to fix #260.  Warning: I'm doing mimicry cut-and-paste and have no idea of the implications for other platforms.
Merge pull request #261 from nejucomo/260.install_alethzero_on_unix

260.install alethzero on unix