Fix #3408 - enable puppetd http compression

This patch adds HTTP response decompression (both gzip and deflate streams).
This feature is disabled by default, and enabled with --http_compression.
This feature can be activated only if the local ruby version supports the
zlib ruby extension.

HTTP response decompression is active for all REST communications and file
sourcing.

To enable http compression on the server side, it is needed to use a
reverse proxy like Apache or Nginx with adhoc configuration:

Nginx:
gzip on;
gzip_types text/pson text/json text/marshall text/yaml application/x-raw text/plain;

Apache:
LoadModule deflate_module /usr/lib/apache2/modules/mod_deflate.so
AddOutputFilterByType DEFLATE text/plain text/pson text/json text/marshall text/yaml application/x-raw

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>