CentOS7安装Mono
先配置：
yum install yum-utils rpm --import "http://keyserver.ubuntu.com/pks/lookup?op=get&search=0x3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF" yum-config-manager --add-repo http://download.mono-project.com/repo/centos/
配置完后怎么安装呢？上面的地址给了一句话：
Run a package upgrade to upgrade existing packages to the latest available. Then install Mono as described in the Usage section.
查看Usage是这样的：
The package mono-devel should be installed to compile code.
The package mono-complete should be installed to install everything - this should cover most cases of “assembly not found” errors.
The package referenceassemblies-pcl should be installed for PCL compilation support - this will resolve most cases of “Framework not installed: .NETPortable” errors during software compilation.
The package ca-certificates-mono should be installed to get SSL certificates for HTTPS connections. Install this package if you run into trouble making HTTPS connections.
The module mono-xsp4 should be installed for running ASP.NET applications.
那么问题来了，到底怎么安装？？？其实上面的意思就是这样：
yum upgrade yum install mono-complete
在长时间的安装之后，通过这个地址的文档来验证安装状态：
http://www.mono-project.com/docs/getting-started/mono-basics/
