Bug 3967: ipc/Kid.cc compilation failure: 'time' was not declared in this scope

Function time() comes from <time.h>, so add the necessary #include.
Source Maintenance: move 3.HEAD snapshot build to website scripts
Remove many uses of String::defined()

Making it private to String:: so that we can easier avoid dealing with
NULL buffer vs "" problems in future.
Bug 3970: max_filedescriptors disabled due to missing setrlimit
Missing include from rev.13143
Fix const-correctness in rev.13143
Fix other issues in rev.13143
Bug 3782: Digest authentication not obeying nonce_max_count