fixed typo

v2/libtpctac/tacx.c

@@ -669,7 +669,7 @@ int tacSetX(
     statusSet(status, __func__, __FILE__, __LINE__, TPCERROR_OK);
     return TPCERROR_OK;
   }
-  /* Check that some x values are there to beging with */ 
+  /* Check that some x values are there to begin with */ 
   if(!tacIsX(d)) { 
     statusSet(status, __func__, __FILE__, __LINE__, TPCERROR_NO_X);
     return TPCERROR_NO_X;