#479: avoid issues due to trailing path separators

Cut trailing separators when converting from string to sgpath.
Also, SGPath::fix does NOT replace ":". It only replaces "\" with "/",
so the "i!=1" check for Windows made no sense (rule #9: never believe
a source code comment).

simgear/debug/debug_types.h

@@ -1,5 +1,5 @@
 /** \file debug_types.h
- *  Define the various logging classes and prioritiess
+ *  Define the various logging classes and priorities
  */
 
 /** 
@@ -30,7 +30,7 @@ typedef enum {
     SG_AI          = 0x00080000,
     SG_ENVIRONMENT = 0x00100000,
     SG_SOUND       = 0x00200000,
-    SG_UNDEFD      = 0x00400000, // For range checkingng
+    SG_UNDEFD      = 0x00400000, // For range checking
 
     SG_ALL         = 0xFFFFFFFF
 } sgDebugClass;