multiple exceptions in 7.1

[David Hough 754R work <754r@xxxxxxxxxxx>]

Discussion of multiple exceptions: draft 1.5.0 is fuzzy about cases of multiple
exceptions arising in one operation, and overspecifies the behavior of
signalException which is itself problematic in every other aspect as well.    
Leaving aside whether 5.6.2 should be included at all, here is a rewrite that's
intended to focus on what's important:

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Existing text:

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An invocation of the signalException operation of 5.6.2 might signal any 
combination of exceptions. 
For an invocation of any other operation required by this standard, at most two 
exceptions might be signaled, in just these combinations: overflow followed by 
inexact, and underflow followed by inexact.

The inexact exception is signaled if the overflow exception receives default 
handling, and might be signaled if the underflow exception receives default 
handling (see 7.5).

In general, when an operation signals more than one exception, none of which 
have alternate exception handling enabled, each signaled exception will receive 
its default handling.

When an operation signals more than one exception, some or all of which have 
alternate exception handling enabled, alternate exception handling will be 
invoked for the most important exception, and languages define whether other 
signaled exceptions receive default handling, alternate handling, or are 
ignored.    
Exceptions are listed in this clause in order of decreasing importance 
(invalid, divideByZero, overflow, underflow, inexact).

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Revised text:

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An invocation of the signalException operation (5.6.2) might signal any 
combination of exceptions. 
Language standards define behavior of signalException when it signals more than 
one
exception.   [This sentence could be in 5.6.2 replacing "The order in which the
exceptions are signaled is unspecified."]

For an invocation of any other operation required by this standard, at most one 
exception might be signaled directly; additional exceptions might be signaled 
by default or
alternate exception handling.
Default exception handling for overflow (7.4) signals the inexact exception.
Default exception handling for underflow (7.5) signals the inexact exception 
if the default result is inexact.

An invocation of the restoreFlags operation (5.7.4) might raise any combination 
of
status flags directly, and the signalException operation (5.6.2) might raise any
combination of status flags indirectly through exception handlers.
For an invocation of any other operation required by this standard,
when all exceptions are handled by default, at most two status flags can be 
raised,
underflow with inexact (7.4) or overflow with inexact (7.5).