Repair broken CHECK directives and use CHECK-LABEL to improve test failures.

Sometimes, we do `CHECK: some-procedure-name` to separate tests within the same file from each other.
While mostly fine, there are edgecases that cause this to produce slightly confusing error messages
in the event of failure, something for which FileCheck has a shiny feature for avoiding:
http://llvm.org/docs/CommandGuide/FileCheck.html#the-check-label-directive

Additionally, two typo'd CHECK directives were repaired. (one missing a colon, so it wasn't really
a CHECK, and one that was just a comment with the name of the instruction that was to be checked for).