PR# 14681 Call to {PLAIN_TEXT_FILE}.read_double returns garbage if next value not real

A call to {PLAIN_TEXT_FILE}.read_double (or read_real) should fail if the
next characters in the file do not represent a real number.  Instead, it
returns a garbage value (8.9959041872935432e-309 for read_double and
3.93962e-38 for read_real).  Test program attached.

The problem appears to be that routines `file_gi', `file_gr' and `file_gd'
(in file.c) all check that the returned value of fscanf < 0.  But if the
conversion fails but there is no EOF, fscanf will return 0 (number of items
successfully converted).  So instead of failing, the routine returns the
value of the uninitialized local.

Problem discovered when lint reported possible use of locals before they were
set.

Compile attached program.
Create input file "abc" with a single line whose contents are "weasel".
Run program.
Prints garbage values instead of raising an exception.

In PLAIN_TEXT_FILE, we have `is_sequence_an_expected_numeric' which is currently not exported. If we were to export it, we could use it for letting the user know about the failure to read.

However for the real/double variant, it is harder and requires that we put a rescue clause in `read_double' and `read_real' to catch failures, so I'll need to modify those externals so that we get a better idea of what the failure is.

You should either raise an exception or add a way for the caller to check that
the read_double, read_real or read_integer operation failed to successfully
read a real or integer.  Otherwise, a file with unexpected contents can cause
an infinite loop.  This applies also to read_integer, which should not return 0
if it can't read a valid integer from the file (unless there is another 
boolean to indicate whether the read was successful).

Note also that the obsolete routines (and their callers in EiffelBase)
should probably be removed, or at least marked obsolete.  The Eiffel routines
are:

   {CONSOLE}.console_readint
   {CONSOLE}.console_pi
   {PLAIN_TEXT_FILE}.file_pi
   {PLAIN_TEXT_FILE}.file_gi

The C routines are:

   file_gi          (in file.c)
   console_readint  (in console.c)

For `file_gi' which is not used anymore, the Eiffel equivalent returns 0. Should we return 0.0 for DOUBLE/REAL, or raise an exception?

Attachments for problem report #14681