Fix compiler warning in config assert() on 64 bit architecture (#158)

* Replace the following code that was used to force an assert:
configASSERT( pxTCB->ulNotifiedValue[ uxIndexToNotify ] == ~0UL );

with:
configASSERT( xTickCount == ( TickType_t ) 0 );

Because the former generates a warning on 64-bit architectures.
diff --git a/tasks.c b/tasks.c
index ef1bde1..0724291 100644
--- a/tasks.c
+++ b/tasks.c
@@ -4887,7 +4887,7 @@
                     /* Should not get here if all enums are handled.

                      * Artificially force an assert by testing a value the

                      * compiler can't assume is const. */

-                    configASSERT( pxTCB->ulNotifiedValue[ uxIndexToNotify ] == ~0UL );

+                    configASSERT( xTickCount == ( TickType_t ) 0 );

 

                     break;

             }

@@ -5030,7 +5030,7 @@
                     /* Should not get here if all enums are handled.

                      * Artificially force an assert by testing a value the

                      * compiler can't assume is const. */

-                    configASSERT( pxTCB->ulNotifiedValue[ uxIndexToNotify ] == ~0UL );

+                    configASSERT( xTickCount == ( TickType_t ) 0 );

                     break;

             }