Worked around a bug of Boost.Build.

* jamroot: Removed `check` target.
* test/jamfile: Newly added.
* test/unit/jamfile:
  * Removed `default-build properties`.
  * Obfuscated the target name to work around a bug of Boost.Build. See the
    comment for detail.
* test/unit/exception/uncaught_exception_run.cpp: Tweaked a message of an
  exception.