case sensiitveness of package name

[DustinCheng]

cnpm handles package name in case insensitive way while npm is case sensitve.
i.e.
cnpm info filelist gets same result as cnpm info FileList but
npm info filelist is different from npm info FileList

Some package, like filelist, is messed up in cnpmjs.org due to this issue.

[DustinCheng]

cnpm@7.1.0

[fengmk2]

#1699