This is a follow-up of previous backticks replacement commits. This
replaces backticks command substitutions in remaining ext config M4
files, phpize, and configure.ac with the recommended $(...).
Note that $(...) still does not work on some obsolete shells that ship
with Solaris 10, for example. Elsewhere they should work. However, for
these obsolete shells Autoconf also re-executes the shell script under
the supported shell so it can make them work regardless.
Additionally, few comments CS are also adjusted to not cause confusion
when searching for backticks usages and one indentation sync done.
As of Autoconf 2.72 the backticks in macro help texts are also replaced
with single quotes.
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.
