Add path::is_absolute.

This is actually not entirely trivial since we can have a path that starts with a slash but includes more ‘..’ components than there are actual directories in the path.

Frameworks/io/src/path.cc

@@ -178,6 +178,17 @@ namespace path
 		return !path.empty() && path[0] == '/' ? normalize(path) : normalize(base + "/" + path);
 	}
 
+	bool is_absolute (std::string const& path)
+	{
+		if(!path.empty() && path[0] == '/')
+		{
+			std::string p = normalize(path);
+			if(p != "/.." && p.find("/../") != 0)
+				return true;
+		}
+		return false;
+	}
+
 	std::string with_tilde (std::string const& p)
 	{
 		std::string const& base = home();

Frameworks/io/src/path.h

@@ -21,6 +21,7 @@ namespace path
 
 	PUBLIC std::string join (std::string const& base, std::string const& path); // this will normalize the (resulting) path
 
+	PUBLIC bool is_absolute (std::string const& path);
 	PUBLIC std::string with_tilde (std::string const& path);        // /Users/me/foo.html.erb → ~/foo.html.erb
 	PUBLIC std::string relative_to (std::string const& path, std::string const& base); // /Users/me/foo.html.erb (arg: ~/Desktop) → ../foo.html.erb