ENH: Since install works on Windows too, remove the UNIX

Source/cmInstallFilesCommand.h

@@ -52,7 +52,7 @@ public:
    */
   virtual const char* GetTerseDocumentation() 
     {
-    return "Create UNIX install rules for files.";
+    return "Create install rules for files.";
     }
   
   /**

Source/cmInstallProgramsCommand.h

@@ -52,7 +52,7 @@ public:
    */
   virtual const char* GetTerseDocumentation() 
     {
-    return "Create UNIX install rules for programs.";
+    return "Create install rules for programs.";
     }
   
   /**

Source/cmInstallTargetsCommand.h

@@ -53,7 +53,7 @@ public:
    */
   virtual const char* GetTerseDocumentation() 
     {
-    return "Create UNIX install rules for targets.";
+    return "Create install rules for targets.";
     }
   
   /**