add FileDelete function to spidermonkey takes 1 param, the path of the file to delete, using / as the path seperator, regardless of unix vs. windows.  returns true is it was successfull, otherwise false

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@3854 d0543943-73ff-0310-b7d9-9358b9ac24b2