apache: include mod_{filter,access_compat,version} by default

We should strive to make our Apache configs compatible with both Apache 2.2 and
2.4; it takes only a little effort and it will ease migration to trusty
considerably. So include mod_version, mod_filter and mod_access_compat by
default.

mod_filter is needed for AddOutputFilterByType on 2.4. we already enable it on
all the app servers.

Impact:

* On Trusty:
  - mod_version is compiled into the server, so including it is a no-op.
  - mod_access_compat will be enabled.
  - mod_filter will be enabled.
* On Precise:
  - mod_version will be enabled.
  - mod_access_compat is not relevant / doesn't exist; no-op.
  - mod_filtered will be enabled.

Change-Id: I5abf0181094eda7f96d14571aa7b599d2c214070
Merge "apache: include mod_{filter,access_compat,version} by default" into production