Getting the const-correctness of Object sorted once and for all

[Stewart Gordon]

http://d.puremagic.com/issues/show_bug.cgi?id=1824

This has gone on for too long.

Object.toString, .toHash, .opCmp and .opEquals should all be const.  (It's also been 
stated somewhere that they should be pure and nothrow, or something like that, but I 
forget where.)

This makes it a nightmare to use const objects in data structures, among other things, at 
best forcing the use of ugly workarounds.  There are probably other, more serious effects 
of this that can't easily be worked around.

It seems that the main obstacle is rewriting the relevant methods in std.stream.  The 
current implementation doesn't make sense anyway - reading the entire contents of a file 
is certainly not the way to generate a hash or string representation of the stream.  I'm 
thinking the hash should probably be the stream handle, and the string representation 
could perhaps be the full pathname of the file.  Of course, what it should be for non-file 
streams is another matter.  (This would be a change at the API level, but when the API's 
as fundamentally flawed as this....)

Are there any other bits of druntime/Phobos that need to be sorted out before these 
methods can be declared const/pure/nothrow once and for all?

Stewart.