When the XPCOM_DEBUG_BREAK environment variable is already set, don't override it. This will make assertions fatal again on the leak test tinderboxes. (Bug 463681) r=ted.mielczarek

build/leaktest.py.in

@@ -75,7 +75,8 @@ if __name__ == '__main__':
     browserEnv = dict(os.environ)
 
     browserEnv["NO_EM_RESTART"] = "1"
-    browserEnv["XPCOM_DEBUG_BREAK"] = "warn"
+    if not "XPCOM_DEBUG_BREAK" in browserEnv:
+        browserEnv["XPCOM_DEBUG_BREAK"] = "stack"
     if automation.UNIXISH:
         browserEnv["LD_LIBRARY_PATH"] = os.path.join(SCRIPT_DIR, DIST_BIN)
         browserEnv["MOZILLA_FIVE_HOME"] = os.path.join(SCRIPT_DIR, DIST_BIN)