Simplify XDG Base Directory support code

Capitalize app name in the paths.

libaegisub/unix/path.cpp

@@ -36,28 +36,12 @@ std::string home_dir() {
 	throw agi::EnvironmentError("Could not get home directory. Make sure HOME is set.");
 }
 
-std::string xdg_config_home_dir() {
-	const char *env = getenv("XDG_CONFIG_HOME");
+std::string xdg_dir(const std::string &environment_variable,
+                    const std::string &fallback_directory)
+{
+	const char *env = getenv(environment_variable.c_str());
 	if (env && *env) return env;
-
-	agi::fs::path home = home_dir();
-	return (home/".config").string();
-}
-
-std::string xdg_cache_home_dir() {
-	const char *env = getenv("XDG_CACHE_HOME");
-	if (env && *env) return env;
-
-	agi::fs::path home = home_dir();
-	return (home/".cache").string();
-}
-
-std::string xdg_data_home_dir() {
-	const char *env = getenv("XDG_DATA_HOME");
-	if (env && *env) return env;
-
-	agi::fs::path home = home_dir();
-	return (home/".local/share").string();
+	return fallback_directory;
 }
 #endif
 }
@@ -69,10 +53,10 @@ void Path::FillPlatformSpecificPaths() {
 	agi::fs::path prev_dir = home/".aegisub";
 	if (!boost::filesystem::exists(prev_dir))
 	{
-		agi::fs::path xdg_config_home = xdg_config_home_dir();
-		agi::fs::path xdg_cache_home = xdg_cache_home_dir();
-		SetToken("?user", xdg_config_home/"aegisub");
-		SetToken("?local", xdg_cache_home/"aegisub");
+		agi::fs::path xdg_config_home = xdg_dir("XDG_CONFIG_HOME", (home/".config").string());
+		agi::fs::path xdg_cache_home = xdg_dir("XDG_CACHE_HOME", (home/".cache").string());
+		SetToken("?user", xdg_config_home/"Aegisub");
+		SetToken("?local", xdg_cache_home/"Aegisub");
 	} else {
 		SetToken("?user", prev_dir);
 	    SetToken("?local", prev_dir);