avoid the error when the /usr/local/man/man8/ not exist.

在使用#make install安装程序的时候,如果目录/usr/local/man/man8/不存在,就出现了如下错误:
#copy man file
cp conf/tsar.8 /usr/local/man/man8/
cp: cannot create regular file `/usr/local/man/man8/': Is a directory
make: *** [install] Error 1