These checks were once relevant for these extensions in PECL and PHP
versions without availability of the checked macros.

Closes GH-4405

Conditional checks were once used for backwards compatibility with
phpize from PHP versions that didn't have this macro call yet.

Closes GH-4376

Normalization include:
- Use dnl for everything that can be ommitted when configure is built in
  favor of the shell comment character # which is visible in the output.
- Line length normalized to 80 columns
- Dots for most of the one line sentences
- Macro definitions include similar pattern header comments now

The Autoconf's default AS_HELP_STRING macro can properly format help
strings [1] so watching out if columns are aligned manually is not
anymore.

[1] https://www.gnu.org/software/autoconf/manual/autoconf.html#Pretty-Help-Strings

This patch removes the so called local variables defined per
file basis for certain editors to properly show tab width, and
similar settings. These are mainly used by Vim and Emacs editors
yet with recent changes the once working definitions don't work
anymore in Vim without custom plugins or additional configuration.
Neither are these settings synced across the PHP code base.

A simpler and better approach is EditorConfig and fixing code
using some code style fixing tools in the future instead.

This patch also removes the so called modelines for Vim. Modelines
allow Vim editor specifically to set some editor configuration such as
syntax highlighting, indentation style and tab width to be set in the
first line or the last 5 lines per file basis. Since the php test
files have syntax highlighting already set in most editors properly and
EditorConfig takes care of the indentation settings, this patch removes
these as well for the Vim 6.0 and newer versions.

With the removal of local variables for certain editors such as
Emacs and Vim, the footer is also probably not needed anymore when
creating extensions using ext_skel.php script.

Additionally, Vim modelines for setting php syntax and some editor
settings has been removed from some *.phpt files.  All these are
mostly not relevant for phpt files neither work properly in the
middle of the file.

This check was added in 0db373883fb073e1773823b236daaf0d3f5a0491 and
greps for a private implementation detail of the postgres headers,
removed in https://github.com/postgres/postgres/commit/3c4768d0d17d4569f2417aa5741e0317404b6c45

It hasn't worked as intended for 12 years, and can safely be assumed to
not be needed.

The $Id$ keywords were used in Subversion where they can be substituted
with filename, last revision number change, last changed date, and last
user who changed it.

In Git this functionality is different and can be done with Git attribute
ident. These need to be defined manually for each file in the
.gitattributes file and are afterwards replaced with 40-character
hexadecimal blob object name which is based only on the particular file
contents.

This patch simplifies handling of $Id$ keywords by removing them since
they are not used anymore.

Configure scripts for extensions look for PDO include files in
$prefix/include/php. This change makes them look into $phpincludedir
instead, which may be different from $prefix/include/php.

configure will now fail if any of the following function is missing:
* PQprepare
* PQexecParams
* PQescapeStringConn
* PQescapeByteaConn

Whitespace changes and a couple of grammar fixes.