process upstream ETag header

fix invalid header logging:

*) fix segfault when a header starts with "\rX"
   and logging is set to info or debug level
*) use %*s instead of %V

FastCGI fixes:

*) continue to parse available fastcgi record after a split header,
   this fixes the erroneous message "upstream prematurely closed connection
   while reading response header from upstream"
*) fix a garbage in a split fastcgi header
*) refactor fastcgi stderr handling

XSLT filter fixes:

*) preserve XML wellFormed field before freeing memory
*) fix libxml2 error message

win32 fixes:

*) ngx_http_set_exten() is always successful since 0.3.46
*) skip URI trailing dots under Win32
*) use caseless regex locations on caseless filesystems: MacOSX, Win32, Cygwin

*) $upstream_cache_status
*) clean cache updating state if a response has uncacheable code or
   cache prohibitive headers

do not test "..." case since it's Win9x family feature only