Added `Class.InstallUtils.php` with `libutil.sh` function (refs #3616)

The `installUtils` shell function, from `libutil.sh`, allows to run
helper methods from the class `InstallUtils` and perform various
operations needed on install or upgrade.

It's a kind of a PHP swiss-army knife for shell scripts...
Support for context directories with special chars (closes #3616)
Merge pull request #664 from eguaj/3.2-A3616

3.2 a3616