Replace FSwitch call with vimscript

autoload/splitopen.vim

@@ -1,11 +1,28 @@
+function s:getFileExtension(filename)
+	return fnamemodify(a:filename, ":e")
+endfunction
+
+function s:getFileRoot(filename)
+	return fnamemodify(a:filename, ":r")
+endfunc
+
+function s:getSwitchExtension(extension)
+	if (a:extension == "cpp")
+		return "h"
+	elseif (a:extension == "h")
+		return "cpp"
+	endif
+endfunc
+
+function s:getSwitchFile(filename)
+	return s:getFileRoot(a:filename) . "." . s:getSwitchExtension(s:getFileExtension(a:filename))
+endfunc
+
+function s:addLeftSplit(filename)
+	execute("vsplit " . s:getSwitchFile(a:filename))
+endfunc
+
 function splitopen#SplitOpenFile(filename)
 	execute("tabedit " . a:filename)
-	let l:file_extension = tolower(fnamemodify(a:filename, ":e"))
-	if l:file_extension == "cpp"
-		execute("FSSplitLeft")
-		execute("wincmd l")
-	elseif l:file_extension == "h"
-		execute("FSSplitRight")
-		execute("wincmd h")
-	endif
+	call s:addLeftSplit(a:filename)
 endfunction