Merge of r4985, r4986, r4987, r4988, r4989, r5002: access_log gzip. *) Access log: fixed redundant buffer reallocation. Previously a new buffer was allocated for every "access_log" directive with the same file path and "buffer=" parameters, while only one buffer per file is used. *) Reopening log files code moved to a separate function. The code refactored in a way to call custom handler that can do appropriate cleanup work (if any), like flushing buffers, finishing compress streams, finalizing connections to log daemon, etc.. *) Access log: the "flush" parameter of the "access_log" directive. *) Configure: added the NGX_ZLIB define. This was introduced for conditional compilation of the code that requires the zlib library. *) Access log: the "gzip" parameter of the "access_log" directive. Note: this requires zlib version 1.2.0.4 or above to work. *) The data pointer in ngx_open_file_t objects must be initialized. Uninitialized pointer may result in arbitrary segfaults if access_log is used without buffer and without variables in file path. Patch by Tatsuhiko Kubo (ticket #268).