This aligns the Node.js server with the previous PHP one in sending `mock.php`as a callback if there's no `callback` parameter in the query string which istriggered by a recently added test. This prevents the request crashing on thatNode.js server and printing a JS error:```TypeError: Cannot read property '1' of null```Closesjquerygh-4764Refjquerygh-4754(cherry picked from commitdf6858d)

Only allow alphanumeric characters & underscores for callback parameters.The change is done both for the PHP server as well as the Node.js-based version.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.Refjquerygh-4764

Only allow alphanumeric characters & underscores for callback parameters.The change is done both for the PHP server as well as the Node.js-based version.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.Refgh-4764Closesgh-4871

Only allow alphanumeric characters & underscores for callback parameters.The change is done both for the PHP server as well as the Node.js-based version.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.Refgh-4764Closesgh-4871(cherry picked froma702746)

Only allow alphanumeric characters & underscores for callback parameters.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.This is a 1.x/2.x version of pRjquerygh-4871Refjquerygh-4764Refjquerygh-4871

Only allow alphanumeric characters & underscores for callback parameters.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.This is a 1.x/2.x version of PRjquerygh-4871.The change doesn't require a release; it's meant at installations testingthe latest state of `1.12-stable` & `2.2-stable` branches.Refjquerygh-4764Refjquerygh-4871

Only allow alphanumeric characters & underscores for callback parameters.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.This is a 1.x/2.x version of PRjquerygh-4871.The change doesn't require a release; it's meant at installations testingthe latest state of `1.12-stable` & `2.2-stable` branches.This change also fixes testing on Travis & on Chrome/Firefox.Refjquerygh-4764Refjquerygh-4871

Only allow alphanumeric characters & underscores for callback parameters.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.This is a 1.x/2.x version of PRgh-4871.The change doesn't require a release; it's meant at installations testingthe latest state of `1.12-stable` & `2.2-stable` branches.This change also fixes testing on Travis & on Chrome/Firefox.Closesgh-4875Refgh-4764Refgh-4871

Only allow alphanumeric characters & underscores for callback parameters.This is only test code so we're not fixing any security issue but it happensoften enough that the whole jQuery repository directory structure is deployedonto the server with PHP enabled that it makes is easy to introduce securityissues if this cleanup is not done.This is a 1.x/2.x version of PRjquerygh-4871.The change doesn't require a release; it's meant at installations testingthe latest state of `1.12-stable` & `2.2-stable` branches.This change also fixes testing on Travis & on Chrome/Firefox.Closesjquerygh-4875Refjquerygh-4764Refjquerygh-4871(cherry picked fromacb7c49)