[RFC] Split I/O routines into two new files, bfdio.c and bfdwin.c

[Klee Dienes <klee at apple dot com>]

The next batch of patches I hope to submit are some extensions to be 
core I/O layer of BFD.

They basically offer three improvements over the current core:

* Support for mutliply-nested layers of archives (for example, an 
'ar'-format library that contains other 'ar'-format libraries, or 
Mach-O fat binaries).

* Support for "user-defined" I/O routines for BFDs --- the user passes 
in a struct containing a set of function pointers to implement 
read/write/seek/close/flush/stat, and have that be used as the basis of 
a BFD.  We use this in our GDB support to allow treating sections of 
memory in the inferior as a BFD, by dispatching the BFD I/O calls 
through the GDB target read/write calls.

* Improved support for "in-memory" BFDs, allowing clients to create 
BFDs out of memory regions and/or mmap, and access them via 
get_section_in_window.

I've got a bit of work to do to clean them up and split them into 
manageable patches; I'll post more on each as I submit them.  One issue 
that arises though:

When I did the work, I found that it was much easier for me to manage 
the I/O code and mmap code if I split it out into separate files 
(particularly the I/O code, as I could iterate through it to make sure 
I'd handle all the clients of a given interface when making a 
modification).

So for example, our bfdio.c contains the following functions: 
bfd_bread, bfd_bwrite, bfd_flush, bfd_tell, bfd_stat, bfd_seek, 
_bfd_io_close, bfd_get_mtime, bfd_get_size (we've removed some of the 
functions from the original implementation, like real_read).

Unfortunately for us, it's not very practical to make diffs between 
source trees where functions have been moved from one file to another.  
So we either need to convince you to make the equivalent split of 
source files, or re-merge our sources into one big file again.

What would your opinion be on a patch to split the existing I/O and 
window code from libbfd.c, opncls.c, and bfd.c into two new files, 
bfdio.c and bfdwin.c?  It would be a purely mechanical patch, just 
moving functions and headers wholesale to the appropriate files.