test for bug 920987

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extra : rebase_source : 0e049c2e25f60bfff2dd45869a770ed9055c9de2
b=921675 use maximum instead of current delay for tail time because delay can increase faster than time passes r=ehsan

--HG--
extra : rebase_source : b74864829e5fa0cdfbd555d93d2c71dd656f2258
b=910174 add DelayNode's tail-time reference as soon as the engine receives sound r=ehsan

This removes the dependence on AllInputsFinished() which didn't return true
for many input types.

The DelayProcessor is no longer continuously reset (bug 921457) and the
reference is now correctly added again when all inputs are finished and then
new inputs are connected.

--HG--
extra : rebase_source : b85c62305a6fcfce57bd40a11edaeaaf2a63c188