Cycles OSL: shader script node

Documentation here:
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/OSL
http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.65/Cycles

These changes require an OSL build from this repository:
https://github.com/DingTo/OpenShadingLanguage

The lib/ OSL has not been updated yet, so you might want to keep OSL disabled
until that is done.

Still todo:
* Auto update for external .osl files not working currently, press update manually
* Node could indicate better when a refresh is needed
* Attributes like UV or generated coordinates may be missing when requested from
  an OSL shader, need a way to request them to be loaded by cycles
* Expose string, enum and other non-socket parameters
* Scons build support

Thanks to Thomas, Lukas and Dalai for the implementation.

intern/cycles/util/util_path.cpp

@@ -170,7 +170,7 @@ bool path_read_binary(const string& path, vector<uint8_t>& binary)
 	return true;
 }
 
-static bool path_read_text(const string& path, string& text)
+bool path_read_text(const string& path, string& text)
 {
 	vector<uint8_t> binary;
 
@@ -184,6 +184,14 @@ static bool path_read_text(const string& path, string& text)
 	return true;
 }
 
+uint64_t path_modified_time(const string& path)
+{
+	if(boost::filesystem::exists(path))
+		return (uint64_t)boost::filesystem::last_write_time(path);
+	
+	return 0;
+}
+
 string path_source_replace_includes(const string& source_, const string& path)
 {
 	/* our own little c preprocessor that replaces #includes with the file