Added Support for Syncronous Testing of Promise Presence

[bbusschots-mu]

While the resolution of a promise is clearly an asynchronous thing, testing for the presence of a promise is not, so it should be possible to test whether or not a given value is a promise using validate() or validate.single().

This very small commit makes that possible by adding an option allowPromises to validate().

The following console output from node run from the project root folder shows the proposed change in action:

cc-dsk-2ss:validate.js bart$ node
> let validate = require('./');
undefined
> // create a custom promise validator
undefined
> validate.validators.promise = function(val, opts){
...     // implicitly pass empty values
...     if(!validate.isDefined(val)) return undefined;
...         
...     // test the passing case
...     if(validate.isPromise(val)){
.....         return undefined;
.....     }
...         
...     // if we got here, we have an error, so return an error message
...     return opts.message || this.message || 'is not a promise';
... };
[Function]
> // create a promise
undefined
> var p = Promise.resolve('thingys');
undefined
> 
> // should throw an error
undefined
> validate.single(p, {presence: true, promise: true});
Error: Use validate.async if you want support for promises
    at validate (/Users/bart/Documents/Temp/fromGitHub/validate.js/validate.js:33:17)
    at Function.single (/Users/bart/Documents/Temp/fromGitHub/validate.js/validate.js:202:14)
    at repl:1:10
    at ContextifyScript.Script.runInThisContext (vm.js:44:33)
    at REPLServer.defaultEval (repl.js:239:29)
    at bound (domain.js:301:14)
    at REPLServer.runBound [as eval] (domain.js:314:12)
    at REPLServer.onLine (repl.js:433:10)
    at emitOne (events.js:120:20)
    at REPLServer.emit (events.js:210:7)
> // should fail validation
undefined
> validate.single('stuff', {presence: true, promise: true}, {allowPromises: true});
[ 'is not a promise' ]
> // should pass validation
undefined
> validate.single(p, {presence: true, promise: true}, {allowPromises: true});
undefined
> 

I could also add the promise validator as a separate pull request?

[coveralls]

Coverage remained the same at 100.0% when pulling ddc1a85 on bbusschots-mu:master into 07f64ec on ansman:master.

[ansman]

This has actually been a long standing bug.

[ansman]

Closed via bfa56eb

[ansman]

A fix has been released in 0.12.0