Merge pull request #19 from baktrius/fix-assert-zero

fix bug in ASSERT_ZERO

channel.c

@@ -23,7 +23,7 @@ shouldn't observably differ in any way other than execution duration.
             fprintf(                                                                         \
                 stderr,                                                                      \
                 "ERROR: Failed: %s\n\tIn function %s() in %s line %d.\n\tErrno: (%d; %s)\n", \
-                #expr, __func__, __FILE__, __LINE__, errno, strerror(errno)                  \
+                #expr, __func__, __FILE__, __LINE__, _errno, strerror(_errno)                  \
             );                                                                               \
     } while(0)