Patches for Borland TDS debugging info

[Troy Rollo]

The attached patch and additional files add support to BFD for recognising 
Borland TDS debugging information. I'll be sticking the copyright 
assignment and employer disclaimer for RMS in the mail tomorrow (I have 
done these previously in early '93 for GDB and GAS, hence also for 
Binutils, but as I understand it I need to do another one now because of 
the new files).

There are a couple of changes in particular that you should probably be 
specifically aware of:

1. I have added a new data element to the BFD structure - 
"opened_for_symbols". TDS is a debugging only format which can either be in 
the executable, or in a separate file. It should *only* be recognised when 
a file is being opened to be read for debugging symbols. A reader is 
expected to set this element to "true" immediately after opening the file 
and before attempting to get BFD to recognise the type of file.

2. In peicode.h, there was a check that assumed that the PE (COFF) header 
in a Win32 executable was exactly 0x80 bytes from the DOS header (AKA the 
start of the file). Unfortunately, this assumption is incorrect. To fix it 
to do the "right" thing would have entailed huge changes due to a structure 
that had been passed through multiple calls assuming this, and some of 
these COFF generic calls would have had to know more about the PE format 
than seemed appropriate, so I commented out this check altogether. This 
shouldn't hurt anything since by the time we get to that check there have 
been other checks which should only match a PE file anyway.

3. I have made no attempt to make TDS work in a heterogeneous remote 
debugging environment.
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