[objc-improvements] Yet another set of fixes committed

[Ziemowit Laski]

Here's what I scribbled into the CVS Log:
- Ensure that when only a single method prototype is available for a 
message,
  use that method's signature in its entirely when constructing the 
call.
  The method-10.m test case checks for that.
- When multiple method prototypes are available (when sending to 'id' or
  'Class'), issue a stern warning and use 'id' for return type and '...'
  for arguments, rather than picking some signature at random. :-(
  Test cases have been modified to accommodate the new wording.
- Fix a duplicate warning, exposed by the comp-types-1.m test case.
- Fix/streamline the handling of method selectors, esp. hashing.  Also,
  simplify the method addition logic.

Please test away!  I will now sync up with HEAD and, if there are no
regressions, will commit that as well.

Thank you,

--Zem
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Ziemowit Laski                 1 Infinite Loop, MS 301-2K
Mac OS X Compiler Group        Cupertino, CA USA  95014-2083
Apple Computer, Inc.           +1.408.974.6229  Fax .5477