We're seeing at least up to 4k in the wild, so increase the limit
somewhat.

See: #939

Print out the rest of the format, changing the error from

  "Unknown format character: {"

to:

  "Unknown format starting at: %{asdf}x"

Fall back to "-" if the handling has not been decided yet.

Fixes: #950
Fixes: #944
Fixes: #918

utils expect to receive SIGHUP).

Fixes: #947

memlevel 8.

Fix testcases which depend on older values.

gzip_window and gzip_memlevel.

Still same pessimal values though.

Fixes: #876

Thanks to new GCC for spotting those.

The size of a regex is a size_t.  Spotted by gcc 4.6

returns random file names

Eventually, we want to be able to do synthetic everywhere, but for
now, mark it as just available in vcl_error.

Fixes: #936

Record the original strdup-ed value so we can free it afterwards.

Fixes: #935

We were accidentially sending an end-chunk in some cases where a
response was bodyless such as for 304s.

Thanks to Chris Davies for spotting them.