Add Platform Support Verification

[mwbrooks]

Overview

The global commands of the PhoneGap CLI must detect whether the system has the platform SDK installed. The command will then execute locally or remotely.

Cordova Public Interface

At the moment, Cordova CLI does not publicly expose an interface to check the platform support.

Solution

The Cordova CLI implementation is minimal.

A short-term action can be to implement the verification functions within the PhoneGap CLI.

A long-term action can be to expose the verification functions in the Cordova CLI.

[mwbrooks]

Blocking #10

[mwbrooks]

Commit e295a33 adds the platform verification.

Issue #29 will coordinate the donation of the code to Cordova CLI.