Merge r1684900, r1687539, r1687680, r1688331, r1688339, r1688340, r1688341, r1688343...

Merge r1684900, r1687539, r1687680, r1688331, r1688339, r1688340, r1688341, r1688343, r1697013, r1697015 from trunk:

mod_substitute: Fix configuraton merge order.
PR 57641 [Marc.Stern]

mod_substitute: follow up r1684900.
Introduce the SubstituteInheritBefore directive to configure the merge order.
This allows to preserve 2.4 and earlier behaviour.

mod_substitute: follow up to r1687539.
Use tristate single inherit_before variable instead of two, according to
wrowe's advices.

mod_substitute: follow up to r1687680.
Fix dir config merger 'over'-write, thanks Bill (again).

Very difficult to read, and therefore was wrong.

Assert that the SubstituteInheritBefore option was explicitly toggled,
and do not default in 2.x to this legacy behavior.

Optimize in all cases that the members are all explicitly initialized.

Useful for 2.2 and 2.4, but trunk will require the subsequent patch.

Increase legibility of the max_line_length behavior, and adjust for
the requirement that all members are initialized explicitly due to
the previous patch.

Net -8 LoC, my usual specialty.

This didn't need to be reinvented; please use established helpers.

mod_substitute: follow up r1688339.
SubstituteInheritBefore is the default in 2.5.x but wasn't for ealier versions.

mod_substitute: follow up r1697013.
Update the doc.
Submitted by: niq, ylavic, ylavic, ylavic, wrowe, wrowe, wrowe, wrowe, ylavic, ylavic
Reviewed/backported by: jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1707039 13f79535-47bb-0310-9956-ffa450edef68