Add Varnish 4 to testing matrix

Add Varnish 4 VCLs

Add Varnish repo

Use separate VCL set for Varnish 4 in tests

Execute APT commands as root

Execute APT commands as root

Travis runs on Ubuntu, not Debian, doh!

Re-add Varnish that fell out

Fix path to Varnish 4 VCLs

Fix string match

Try to limit number of builds

Fix .travis.yml

Set cache debug header in vcl_miss because obj.hits is unreliable

Fix ban VCL

Clean up user context VCL

Add sleep for Varnish 4

Improve Varnish 4 hit/miss calculation

Re-use refresh.vcl from Varnish 3

Use kill -9 and remove sleep

Make user context VCL compatible with Varnish 4

Update docs with Varnish 4 VCLs

Rename varnish directory to varnish-3
Merge pull request #67 from FriendsOfSymfony/varnish-4

Test against Varnish 4