Tweak options for sane library

packages/truffle-core/lib/commands/watch.js

@@ -1,4 +1,5 @@
 const colors = require("colors");
+const commandExistsSync = require("command-exists").sync;
 
 const command = {
   command: "watch",
@@ -22,6 +23,16 @@ const command = {
         /[\/\\]\./ // Ignore files prefixed with .
       ]
     };
+    // Certain large codebases have trouble with the watch command.
+    // Installing watchman resolves some of these issues.
+    if (commandExistsSync("watchman")) {
+      watchOptions.watchman = true;
+    } else {
+      config.logger.log(
+        "If you have trouble using watch, try installing watchman."
+      );
+    }
+
     const watchCallback = filePath => {
       const displayPath = path.join(
         "./",

packages/truffle-core/package.json

@@ -8,6 +8,7 @@
     "async": "2.6.1",
     "chai": "4.1.2",
     "colors": "^1.1.2",
+    "command-exists": "^1.2.8",
     "configstore": "^4.0.0",
     "cpr": "^0.4.3",
     "debug": "^3.1.0",