安装php的ssh2的扩展库，如果出现如下错误：
checking for ssh2 files in default path... not found configure: error: The required libssh2 library was not found. You can obtain that package from http://sourceforge.net/projects/libssh2/ ERROR: `/tmp/pear/download/ssh2-0.11.0/configure --with-ssh2=/usr' failed
解决方法如下：
Installing libssh2 via tar.gz from http://sourceforge.net/projects/libssh2/ help a lot (--with-ssh2=/usr/local/include/).
But "yum install libssh2-devel" is a better idea.
