print fsevents require error when env var set (#605)

Author: vjpr

lib/fsevents-handler.js

@@ -4,7 +4,9 @@ var fs = require('fs');
 var sysPath = require('path');
 var readdirp = require('readdirp');
 var fsevents;
-try { fsevents = require('fsevents'); } catch (error) {}
+try { fsevents = require('fsevents'); } catch (error) {
+  if (process.env.CHOKIDAR_PRINT_FSEVENTS_REQUIRE_ERROR) console.error(error)
+}
 
 // fsevents instance helper functions