Changed execution->call on trace of onRouteRequest

Seems to be a cause of trouble for some Play applications that use
javax.* classes.  Not exactly sure why, but followed suggestion found
here: http://www.eclipse.org/forums/index.php/t/206028/

Converting the 'execution' to a 'call' does not seem to have affected
the tests - all pass.  But it does now cause echo to weave properly into
this test application: https://github.com/andyczerwonka/tyrion

Without this change the aspectj weaver would issue a warning:

"warning javax.* types are not being woven because the weaver option '-Xset:weaveJavaxPackages=true' has not been specified"

Would be displayed and a single cutpoint:
public Option play.api.GlobalSettings+.onRouteRequest(RequestHeader)

Would fail.
Merge pull request #10 from typesafehub/onRouteRequest-fix

Changed execution->call on trace of onRouteRequest