add concurrent tests for our GenericSTM implementation
add check_reads primitive (for opacity checking) and make GenericSTM use it (hopefully temporarily)
fix bug in list iteration
make listsize_ part of List.hh work better for multithreaded. still might be a race (we may need to lock the whole list or something when changing the size variable)
ugh fix more dumb bugs in List.hh
add a ListArray class for testing our linked list. This has O(n) reads and writes (for an array abstraction) which makes it a little hard to use. That said it fits into our existing concurrent testing framework, and has already found bugs in the list implementation