Request.send_error shouldn't load and render the error template

[Ryan J Ollos]

The Request.send_error​ method has a method-scoped import for Chrome and does the work of loading and rendering the error template.

For a normal request the work of rendering a template is done in trac.web.main. I propose having a _send_error method in trac.web.main that does the work of loading and rendering the error template, and have Request.send_error behave more like Request.send.

Request.send_error has rendered the template since it was added in r2957. At that time, the Request.display method (appears to be similar to Request.send) would also render the HDF template. Request.send was added in r3832 and Request.display was removed in r10405 (when ClearSilver support was removed).