Geo Data should check for php_zip extension

Without the php_zip extension enabled/installed, Geo Data doesn't work, because it can't unpack the uploaded zip file. If attempted, the user gets the WSoD.

From a usability standpoint, it would be nice if:

• Upon installation, the Geo Data module checks for the php_zip extension, and informs the user whether or not it is installed/enabled. This warning could appear on the module administration page (Admin » Build » Geo), and it could also appear in the Status Report (Admin » Reports » Status).
• The "Import Shape Data" form on Admin » Build » Geo is disabled whenever the check fails.