Php bindings 

That commit introduce working bindings to PHP. Finally it can be compiled with cmake, and "-DPHP_BINDINGS=ON" option is available. As with other bindings, PHP needs "-DRUN_SWIG=ON" flag to generate .php and other files by SWIG.

PHP binding needs following packages: php, php-devel, or php-dev or whatever the distro naming is, it should contain php-config binary. Since there is no current FindPhp library in cmake, only mentioned php-config is checked.

Finally, i've done some testing on CentOS/SL 6.4 and everything compiles, installs, and works fine, although further testing is needed on other distros.

Comments are welcome.