doc fixups for g++

[Mike Stump <mrs at apple dot com>]

This enhances the documentation for g++ to better match what it  
really does now-a-days.  Notable changes are:

	We don't imply an argument of foo is treated as C++, cause it's not
	We don't imply foo.f is treated as C++, cause it's not
	We explain just what files are treated as C++

Any objections?

mrs $ cat ~/diffs/doc-1.diffs.txt
2006-06-30  Mike Stump  <mrs@apple.com>

        * doc/invoke.texi (Invoking G++): Clarify prose for g++.

Doing diffs in doc:
--- doc/invoke.texi.~1~ 2006-06-29 13:02:17.000000000 -0700
+++ doc/invoke.texi     2006-06-30 11:40:55.000000000 -0700
@@ -1089,15 +1089,13 @@ with the name @command{gcc}).

  @findex g++
  @findex c++
-However, C++ programs often require class libraries as well as a
-compiler that understands the C++ language---and under some
-circumstances, you might want to compile programs or header files from
-standard input, or otherwise without a suffix that flags them as C++
-programs.  You might also like to precompile a C header file with a
-@samp{.h} extension to be used in C++ compilations.  @command{g++} is a
-program that calls GCC with the default language set to C++, and
-automatically specifies linking against the C++ library.  On many
-systems, @command{g++} is also installed with the name @command{c++}.
+However, the use of @command{gcc} does not add the C++ library.
+@command{g++} is a program that calls GCC and treats @samp{.c},
+@samp{.h} and @samp{.i} files as C++ source files instead of C source
+files, and automatically specifies linking against the C++ library.
+This is also useful when precompiling a C header file with a @samp{.h}
+extension for use in C++ compilations.  On many systems, @command{g++}
+is also installed with the name @command{c++}.

 @cindex invoking @command{g++}
 When you compile C++ programs, you may specify many of the same
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