MMDB_LIB_VERSION

[remicollet]

Digging why test suite fail on old RHEL / CentOS 6

+ php --define extension=/builddir/build/BUILDROOT/php-maxminddb-1.5.0-1.el6.remi17.0.x86_64/usr/lib64/php/modules/maxminddb.so /usr/bin/phpunit --bootstrap /builddir/build/BUILDROOT/php-maxminddb-1.5.0-1.el6.remi17.0.x86_64/usr/share/php/MaxMind/Db/Reader/autoload.php --verbose
PHPUnit 5.7.27 by Sebastian Bergmann and contributors.
Runtime:       PHP 7.0.33
Configuration: /builddir/build/BUILD/MaxMind-DB-Reader-php-bd436094fc0a9b0558a899fb80b0ae34fe1808a0/phpunit.xml.dist
....................F................                             37 / 37 (100%)
Time: 39 ms, Memory: 13.00MB
There was 1 failure:
1) MaxMind\Db\Test\Reader\ReaderTest::testV6AddressV4Database
Failed asserting that exception of type "\InvalidArgumentException" is thrown.
FAILURES!
Tests: 37, Assertions: 363, Failures: 1.

I found this is related to libmaxmindb 1.1.1 in EPEL
https://apps.fedoraproject.org/packages/libmaxminddb

This PR simply expose the MaxMind\\Db\\Reader::MMDB_LIB_VERSION to userland, and thus allow to skip this test (can probably be use later for future change in the library).

[oschwald]

Thanks! I merged from the command line.