Add automatic installation of benchmark-init

[pierre-rouleau]

PEL does not currently have any logic to support installation of benchmark-init.

It would be beneficial to do so because benchmark-init must be treated specially and must go into the PEL utils directory instead of the normal elpa directory.

It is better to install it inside utils because:

• installation of benchmark-init does not increase the number of directories (and the load-path) when it is installed inside utils, therefore the installation of benchmark-init does not influence Emacs startup time.
• It can then be used in both normal and fast startup modes without special file manipulation.

It should also be taken from utils (and not from utils-graphics) even in graphics mode, allowing code iniside init.el to ignore the Emacs mode.

This means that special logic will have to be used inside pel-cleanup.