OpenLayers.Request: let us choose whether we want to run callbacks or not (without duplicating code)

[fvanderbiest]

The following patch moves a portion of the code from the "issue" method to a "runCallbacks" method, which gives application developers the choice to manually execute runCallbacks (eg: when the user accepts to load a heavy response from a server) without duplicating OpenLayers's code.

Tests pass on FF3/linux.

[elemoine]

openlayers_ticket2218_r9616_A1.diff uses "this" where it makes sense. I'm confirming that the tests pass on FF3, IE8, Safari 4 and Opera 9.24. François, tell me if the patch works for you.

[fvanderbiest]

Works great! Thank's Eric. Please commit.

[fvanderbiest]

runCallbacks now uses the standard requestUrl options key instead of url

[elemoine]

closed with [9621]