Composer support related changes. These are being included for testing.

Add cusomization of composer.json to support module-installer-plugin during install

Add checks for OpenSSL and JSON to installer, as those are needed for composer. JSON is normally part of PHP, but due to an odd clause in its license, some distributions (such as debian and derivatives) package it separately.

Add a composer.phar to xoops_lib.

Add Xoops\Core\ComposerUtility.php that provides a mechanism to invoke composer to run commands under program control.
Merge upstream/master
Remove unbound version constraints
Correct issue on Windows systems

Add to, rather than replace, environment, otherwise the process created with proc_open will not be able to access TCP/IP stack -- no network.  Use putenv() to set the required variable, then let proc_open inherit the whole env from PHP.
Fix namespace issue eported by scrutinizer
Merge pull request #136 from geekwright/master

Composer support - for testing