Add support for 64-bit numbers in increment/decrement operations

[reva2]

Add support for 64-bit numbers in increment/decrement operations.

Fixes #58

[mkoppanen]

Hmm, zend_parse_parameters "l" expects "long" as the type so I am not sure how this behaves on 32bit

[reva2]

Hello Mikko.

I fixed issue with signed values as a param for increment/decrement functions. Now tests related to increment/decrement operations passing successfully.

I'm not expert in C/C++ so I'm also not sure how it will behaves on 32bit. But because for param 'initial' you use the same type and zend_parse_parameters mask I think it should work also with param 'offset'. If you have better suggestions I will be glad to hear it.

Related to failed travis build. I've checked build results and found that it the same as results for master branch. It fails only on new test which was added in one of latest commits. I thinks this issue is not related to my changes.

[sodabrew]

Thanks for the original contribution here! I've prepared a new PR to do this more concisely. Closing and will be resolved in php-memcached 3.0.0.