[PATCH] Support APR 1.4 for building on CentOS 7

Dear devs,

I propose a patch restoring support for APR 1.4 so that svn 1.14 can be
built and packaged on CentOS 7.

The WANdisco folks continue to package svn for a variety of target
systems. Packaging for CentOS 7 which has APR 1.4.8, they ran into the
problem that just before svn 1.14.0 we bumped the dependency requirement
to APR 1.5.0 and removed support for older APR versions.

Here's the change we made:
> r1874094 | jamessan | 2020-02-17 03:49:42
> Require at least version 1.5 of APR
>
> Since r1874057, the apr_pescape_shell() API is being used to escape filenames
> when invoking $SVN_EDITOR. This was added to APR in 1.5.0, released on
> 2013-11-13.
>
> * INSTALL
> (): Document new minimum APR version
>
> * build/generator/gen_win_dependencies.py
> (_find_apr): Bump minimal_apr_version to 1.5.0
>
> * configure.ac
> (APR_VER_REGEXES): Bump minor version in 1.x regex to 1.5
>
> * get-deps.sh:
> (APR_VERSION): Specify 1.5.0 as default version
>
> * subversion/include/private/svn_dep_compat.h
> (apr_time_from_msec): Removed, since it's provided by APR 1.4.0 or later
>
> * subversion/include/svn_types.h
> (apr_hash_this_key, apr_hash_this_key_len, apr_hash_this_val): Remove
> prototypes, since they're provide by APR 1.5.0 or later
>
> * subversion/libsvn_subr/iter.c
> (hash_do_baton): Remove condition requiring APR 1.4.0 to define this type
> (svn_iter_apr_hash): Remove pre-APR 1.4.0 code
> (apr_hash_this_key, apr_hash_this_key_len, apr_hash_this_val): Remove
> definitions, since they're provided by APR 1.5.0 or later
>
> * subversion/libsvn_subr/pool.c
> (apr_pool_create_unmanaged_ex): Remove conditional alias to
> apr_pool_create_core_ex, for APR versions < 1.3.3

The context is we'd recently started using apr_pescape_shell() in
r1874057, shortly afterwards changing to using apr_escape_shell()
instead, and those escaping functions are new in 1.5.0.

Ian at WANdisco told me:
> The dependencies we have issues with are apr and apr-util as 1.14 requires at least APR 1.5 and Red Hat ship 1.4.8 in EL7. I tried ignoring the version and using the old apr but it doesn't compile due to some missing symbols.
>
> Because of this if we want to ship any 1.14 build for EL7 we have to build our own (later) APR and APR-Util packages which in turn means libserf and apache httpd would need to link against these too.

They are looking for a more self-contained solution.

I propose adding support more or less as in the attached patch. It:

   - reverts r1874094, thus restoring the support we had for APR 1.4
(and even 1.3 by the look of it), but we never had backward
compatibility support for apr_escape_shell();

   - adds a local copy of the 'apr_escape_shell()' function, copied
from APR 1.7.0.

One adjustments is needed before this is ready to commit: I must make
the 'apr_escape_shell' part conditional on APR version. Note also that
the support for 'apr_escape_shell()' adds 4 files, as that's how the
code was laid out in APR. We could combine them but I preferred to copy
it as exactly as possible.

If this is an acceptable approach, I would propose it for backport to a
1.14.x point release.

WANdisco would prefer to package our upstream svn source release exactly
rather than patch it in their packaging, and that is why I am proposing
adding this support.

Of course I understand that APR pre-1.5 is pretty old and the argument
to not complicate the current code with too much backward compatibility
support code. So the question is whether this is too much or whether
supporting building on distros like CentOS 7 out of the box is the
better option.

- Julian