Construct 2 Release r251

We had a few reports from r250 of crashes on startup. We're still not quite sure what's behind this, but we've done some upgrades to our build process since we suspect it may be related to that. Since this is an essential issue to fix, if this resolves the problem we will probably release another stable update to ensure everyone can use the latest version of Construct 2.

Secondly there have been some reports that appear to indicate a recent Windows update regressing performance opening dialogs for very large projects. Based on the timing, the fact the performance regression appears to be in Windows itself, and potentially involves a large number of system calls, we are beginning to suspect this might actually be related to the Meltdown vulnerability. The mitigation patches that have been rushed out have been known to have a major performance impact in system-call heavy code, particularly with older CPUs. To minimise the performance regression we have modified the way icons are created in "Don't show unique icons" mode. (You must choose this mode in Preferences to activate the workaround.) In this mode we make far fewer calls in to Windows which we hope solves the issue; however most of our machines are modern and don't show any serious problem, and Meltdown's mitigations disproportionately affect older CPUs, so we're keen to hear feedback from users particularly with older systems to see if this helps improve the situation.