运行：
install.packages("RCurl")
得到这样的结果：
> I have some problem in running R-cran's Demography package.
> The hmd.mx function need Rcurl. I tried to install RCurl, but meet the following error:
> *************************************************
> ...
> * installing *source* package ‘RCurl’ ...
> checking for curl-config... no
> Cannot find curl-config
> ERROR: configuration failed for package ‘RCurl’
> * removing ‘/home/z/R/i686-pc-linux-gnu-library/2.12/RCurl’
> ...
> *************************************************
解决方案：
sudo apt-get install libcurl4-gnutls-dev