Upstream: fixed X-Accel-Expires/Cache-Control/Expires handling. Previously, if caching was disabled due to Expires in the past, nginx failed to cache the response even if it was cacheable as per subsequently parsed Cache-Control header (ticket #964). Similarly, if caching was disabled due to Expires in the past, "Cache-Control: no-cache" or "Cache-Control: max-age=0", caching was not used if it was cacheable as per subsequently parsed X-Accel-Expires header. Fix is to avoid disabling caching immediately after parsing Expires in the past or Cache-Control, but rather set flags which are later checked by ngx_http_upstream_process_headers() (and cleared by "Cache-Control: max-age" and X-Accel-Expires). Additionally, now X-Accel-Expires does not prevent parsing of cache control extensions, notably stale-while-revalidate and stale-if-error. This ensures that order of the X-Accel-Expires and Cache-Control headers is not important. Prodded by Vadim Fedorenko and Yugo Horie.

/* XPM */
static char * nginx_xpm[] = {
"16 16 2 2",
/* colors */
"   c none",
"GG c #009900",
/* pixels */
"                                ",
"        GGGGGGGGGGGGGGGG        ",
"        GGGGGGGGGGGGGGGG        ",
"      GGGGGGGGGGGGGGGGGGGG      ",
"      GGGGGG        GGGGGG      ",
"    GGGGGG            GGGGGG    ",
"    GGGGGG                      ",
"  GGGGGG      GGGGGGGGGGGGGGGG  ",
"  GGGGGG    GGGGGGGGGGGGGGGGGG  ",
"    GGGGGG    GGGGGGGGGGGGGG    ",
"    GGGGGG            GGGGGG    ",
"      GGGGGG        GGGGGG      ",
"      GGGGGGGGGGGGGGGGGGGG      ",
"        GGGGGGGGGGGGGGGG        ",
"        GGGGGGGGGGGGGGGG        ",
"                                "
};