Support for svm and correction for scriptcs mono bug #840.

The ``-script`` parameter is required for the following scriptcs & mono issue - **Error running scriptcs when the full path to the file is provided [#840] (https://github.com/scriptcs/scriptcs/issues/840)**.

On Windows with svm installed, shims are used to hook up the correct version of scriptcs. The shim has a scriptcs.cmd (batch file) entry point. Sublime normally looks for scriptcs.exe to execute. To force Sublime to look for both scriptcs.exe (vanilla install) and scriptcs.cmd (svm install), the ``"shell": true`` addition is required to the ``ScriptCs.sublime-build`` file.

This has been tested on Windows with chocolatey installed scriptcs and with svm installed scriptcs. It has been tested on Ubuntu 14.10 with svm installed scriptcs. The ``"shell": true`` addition is scoped only to the Windows platform.