Fixes bug where pnacl-sz was not checking if the inserted type matched
the element type of the corresponding vector. Also fixes operand look
up (within a function) to error recover rather than always die with a
fatal error.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4313
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1357273004 .