Misc. typos

+ some are doxy others are just comment code.  
+ some minor whitespace and grammatical tweaks. 
+ app/SCL/* typos have also been submitted upstream (https://github.com/stepcode/stepcode/pull/366). So it's ok to merge them in to master.

src/Gui/SoFCSelection.cpp

@@ -840,7 +840,7 @@ SoFCSelection::redrawHighlighted(SoAction *  action , SbBool  doHighlight )
 SbBool 
 SoFCSelection::readInstance  (  SoInput *  in, unsigned short  flags )
 {
-    // Note: The read in document name can be false, so the caller must ensure pointing to the correct documemt
+    // Note: The read in document name can be false, so the caller must ensure pointing to the correct document
     SbBool ret = inherited::readInstance(in, flags);
     return ret;
 }