Fixes for libmemcached 1.0.18 build problems


@wolfsage 

This is the quick fix to build issues with libmemcached 1.018, by ignoring missing autoconf tools.
It also fixes the MacOSX build issue in libmemcached.

I have tested the build successfully on Fedora 19 and CentOS 6.5, both x86_64, and MacOSX 
Yosemite with Xcode 5.1.1.  I also ran 'make test' with a local memcached on the Fedora host,
successfully.