Added comments in all.js explaining the different cms modes - part of bug 449681. r=vlad

modules/libpref/src/init/all.js

@@ -128,6 +128,8 @@ pref("browser.chrome.image_icons.max_size", 1024);
 
 pref("browser.triple_click_selects_paragraph", true);
 
+// 0 = Off, 1 = Full, 2 = Tagged Images Only. 
+// See eCMSMode in gfx/thebes/public/gfxPlatform.h
 pref("gfx.color_management.mode", 0);
 pref("gfx.color_management.display_profile", "");
 pref("gfx.color_management.rendering_intent", 0);