* doc/invoke.texi (-fno-nil-receivers): Tidied up line to remove
        underfull hbox in DVI output.
        (-fobjc-class-cxx-cdtors): Same change.
        (-fobjc-exceptions): Tidied up documentation.  Explain what the
        option does, but moved the (lenghty) description of the exception
        syntax into objc.texi.
        (-fobjc-gc): Explain that the option is not useful with the GNU
        runtime.
        (-fzero-link): Explain that the GNU runtime always works in
        "zero-link" mode.
        * doc/objc.texi: All sections: simplified @node declarations
        removing specification of next, previous, up node.
        (Objective-C): Updated introduction.
        (Garbage Collection): Updated.  The bohem-gc library is now
        included in gcc itself.  Mention that this section only applies to
        the GNU Objective-C runtime.
        (compatibility_alias): Small tidy up.
        (Exceptions): New section mostly containing text previously in the
        description of the -fobjc-exception command-line option.
        (Synchronization): Same.

From-SVN: r164586