New Memory Manager for PHP7

Hi,

Please take a look into the proposed new Memory Manager for PHP:

https://github.com/php/php-src/pull/777

The patch provides visible performance improvement on real life apps
(tested on Linux 32 and 64 bit). It's based on ideas mainly borrowed from
jemalloc and tcmalloc.

I hope, the patch must implement all the features of previous memory
manager except for "overridable storage", but I might miss something.

It would be great if experienced people could analyze the sources and give
their opinion.

Thanks. Dmitry.