Changed BLI_convertstringcode to replace any number of hashes with the frame number.

somefile_##.png -> somefile_01.png
somefile_########-image.png -> somefile_00000001-image.png

Before, A hash at the end of the string would be replaced by a number with 4 characters. This is still default if no #'s are in the string, so nothing has changed.

To use this function from the python api use scene.render.getFrameFilename()

source/blender/blenkernel/intern/particle_system.c

@@ -4552,7 +4552,7 @@ static void particles_fluid_step(Object *ob, ParticleSystem *psys, int cfra)
 		(ob->fluidsimSettings)) { 
 		ParticleSettings *part = psys->part;
 		ParticleData *pa=0;
-		char *suffix  = "fluidsurface_particles_#";
+		char *suffix  = "fluidsurface_particles_####";
 		char *suffix2 = ".gz";
 		char filename[256];
 		char debugStrBuffer[256];