fixed /diag/eval handling of complex expressions
fixed /diag/eval handling of complex expressions

Reference to "Req" was causing error producing unused variable
warnings in some cases.

Now:

wget -O- --post-data='(fun () -> ok end)().' --user=Administrator --password=asdasd http://dn2:8091/diag/eval

works. And even

wget -O- --post-data='menelaus_util:reply_json(Req, [<<"ok">>], 200), done.' --user=Administrator --password=asdasd http://dn2:8091/diag/eval

works too.

Change-Id: Ib2c75525d1f147e0e9255b5ac6e37ac9c1439861
Reviewed-on: http://review.couchbase.org/6897
Reviewed-by: Bin Cui <ed18693fff32c00e22495f4877a3b901bed09041@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

nimishzynga/ns_server,membase/ns_server,t3rm1n4l/ns_server,membase/ns_server,daverigby/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,daverigby/ns_server,daverigby/ns_server,membase/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,vzasade/ns_server,daverigby/ns_server,nimishzynga/ns_server,vzasade/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server,mschoch/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,membase/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,vzasade/ns_server,membase/ns_server,vzasade/ns_server,mschoch/ns_server