suite_aggrs: - added support to gen unions in addition to structs - regenerated struct/union-mixed and nested cases - made rand-sig.lua ignore closing struct/union chars if not opened, effectively reducing number of empty aggregates as it now generated way too much

Daniel Adler <dadler@uni-goettingen.de>
Tassilo Philipp <tphilipp@potion-studios.com>
Olivier Chafik <olivier.chafik@gmail.com>
Erik Mackdanz <erikmack@gmail.com>
Masanori Mitsugi <mitsugi@linux.vnet.ibm.com>
Bernhard Urban-Forster <beurba@microsoft.com>