Loop support for Mono.CSharp.Evaluator Terse Mode

When Terse mode automatically adds a semi-colon to partial inputs it causes inputs like "for (int ii = 0; ii < 3; ii++)", or "while (ii < 3)" to execute immediately with no body in the loop, rather than waiting for further input. 

This pull request fixes that problem by detecting loop expressions using a Regex, and not attempting to complete them by adding a semi-colon.