While it looks nicer without zero 3-rd version number, this should
improve interoperability.  Version string can be parsed or used for
sorting.  And it is easier to handle and less confusing when there
is constant number of version parts.

Moreover, NPM also expects version format with 3 parts.
So ".0" has already been used in Node.js module version.

This also eliminates expressions that incompatible with BSD make, thus fixing
installation of Node.js module on FreeBSD (broken by dace60fc4926).

Added the nxt_unit_version.h dependency.
This closes #214 issue on GitHub.

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