I don't like the previous behaviour where the bytes to hash change
every time the code changes, that may make it difficult to compare
hash() performance changes over time.
Use a fixed number instead, and allow passing an override for a
different length.
Closes GH-6386.
[ci skip]
This patch makes several scripts and PHP development tools files
executable and adds more proper shebangs to the PHP scripts.
The `#!/usr/bin/env php` shebang provides running the script via
`./script.php` and uses env to find PHP script location on the system.
At the same time it still provides running the script with a user
defined PHP location using `php script.php`.
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.
