#[V|A] - Upgrade devtools to 1.6.1. from 1.5

This upgrade is necessary because in old version of devtools, they have specified RCurl as a import dependency whereas only one function install_url is dependent on RCurl.
Merge pull request #2 from varadharajan/devtools_upgrade

#[V|A] - Upgrade devtools to 1.6.1. from 1.5