Merge r756671, r756675, r756678, r756683 from trunk:

Creation of external gzip process fails, if we
try to set the working directory to r->filename.
Use ap_make_dirstr_parent() instead, like in all
other similar places.


Creating the external gzip process fails, because we
call execve() with "gzip" without full path.
Let's look for it in the PATH instead and drop the
passing of the environment. There seems to be no
reason why gzip should need the httpd environment.


Set the content encoding for compressed content
even if we can't detect the content type of the
uncompressed content.


When trying to detect the content type of the
uncompressed content it is often not enough
to read the same number of bytes, we already
read compressed. Since uncompress() allocates a
new buffer, we can increase the number of bytes
to read to the same size, we use in the case,
where the content isn't compressed.

Furthermore zero-terminate the read data to keep
assumptions consistent with the uncompressed case.

Submitted by: rjung
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@765999 13f79535-47bb-0310-9956-ffa450edef68