By default "npm install" switches to non-privileged user to run package scripts
if it is invoked by root.  As a result it may prevent node-gyp from writing to
package directory and break installation of the module.

To disable this switching the --unsafe-perm flag is added.

In most cases it is not needed because Ruby libraries are in the default path.
At the same time, rpath pointing to the default path is prohibited by rpmbuild
on Fedora.

This is related to issue #87 on GitHub.

Since PHP 7, a zend_signal_startup() call is required if the interpreter
was built with ZEND_SIGNALS defined; such a call was added in 3fd76e4ce70a.

However, the zend_signal_startup() export is missing from the PHP library;
as the result, dlopen() fails with the 'Undefined symbol "zend_signal_startup"'
error while loading the PHP module.

Meanwhile, if PHP is built without ZTS, the zend_signal_startup() call can
be omitted; otherwise, the missing call causes segmentation fault.

The PHP fix already was committed to upstream, but we still have to deal
with numerous unpatched versions remaining at large.

See the related PHP bug: https://bugs.php.net/bug.php?id=71041

This closes #184 issue on GitHub.

Now by default "make install" installs the module globally.
The "--local" configure option added for local installation.