PR# 15273 System with several rescue clauses that violates precondition goes into infinite loop

A particular system has precondition checking enabled for all classes, including
classes of EiffelBase.  The system includes several routines with rescue
clauses but only the root creation procedure has a retry.  The system compiles
fine but when executed it goes into an infinite loop (when code is melted,
frozen or finalized - doesn't matter).  The infinite loop consumes CPU but
memory size appears to be stable.

Added eweasel test except033 for this bug.  The test is currently marked "skip"
in the catalog since the test will never finish due to the infinite loop.

This is a very serious bug for us, because we run several of our most critical
systems finalized but with all preconditions on (undetected errors can 
potentially be *very* expensive if something gets fabricated incorrectly, so
we're fairly paranoid about error checking for some systems).

If there is a small set of EiffelBase classes for which disabling precondition
checking will prevent the problem, this might be an acceptable workaround.

Run eweasel test except033 (after removing the "skip" tag in the catalog).

This has been fixed in the repository. (elks rev#264)

Thanks for the report, David. This is indeed a problem in `is_throwing'. I will soon commit the fix as long as tests run through. 

I finalized the test case I previously provided and used dbx to discover that
the infinite loop appears to be in {EXCEPTION}.is_throwing.