Migrate to a "cplusplus" filetype for C++ in vim.

This "cplusplus" filetype permits the sourcing of `cpp.vim`
and `doxygen.vim` as lower-level files from itself.  This should
permit `doxygen.vim` to source from `cpp.vim` and avoid endless
recursion, when handling code-in-comments formatting.

vim/filetype.vim

@@ -0,0 +1,35 @@
+" Cynlib
+" .cc and .cpp files can be C++ or Cynlib.
+au BufNewFile,BufRead *.cc
+	\ if exists("cynlib_syntax_for_cc")|setf cynlib|else|setf cplusplus|endif
+au BufNewFile,BufRead *.cpp
+	\ if exists("cynlib_syntax_for_cpp")|setf cynlib|else|setf cplusplus|endif
+
+" C++
+au BufNewFile,BufRead *.cxx,*.c++,*.hh,*.hxx,*.hpp,*.ipp,*.moc,*.tcc,*.inl setf cplusplus
+if has("fname_case")
+  au BufNewFile,BufRead *.C,*.H setf cplusplus
+endif
+
+function! CheckForADAM()
+  if match(getline(1, min([line("$"), 200])), '^@\(interface\|end\|class\)') > -1
+    if exists("g:c_syntax_for_h")
+      setf objc
+    else
+      setf objcpp
+    endif
+  elseif exists("g:c_syntax_for_h")
+    setf c
+  elseif exists("g:ch_syntax_for_h")
+    setf ch
+  else
+    setf cplusplus
+  endif
+endfunction
+
+" .h files can be C, Ch C++, ObjC or ObjC++.
+" Set c_syntax_for_h if you want C, ch_syntax_for_h if you want Ch. ObjC is
+" detected automatically.
+au BufNewFile,BufRead *.h			setf cplusplus "call CheckForADAM()
+au BufNewFile,BufRead		*.cxx,*.cpp,*.hpp,*.cc,*.h		setf cplusplus
+