Using std::deque here causes problems for libc++ builds; TestTXMgr on
OSX 10.6 opt times out when libc++'d std::deque is used. Running the
test locally shows that the test process consumes gigabytes (!) of
memory and is thus reduced to swapping, rather than making any progress.
libc++'s std::deque also appears to be slightly slower in said test that
even OSX libstdc++'s std::deque. (Admittedly, this test is artificial.)
Let's sidestep the slowness of libc++'s std::deque by rewriting
nsTransactionStack to use nsDeque rather than std::deque. Not only does
this change enable OSX 10.6 tests to pass, it also makes TestTXMgr
significantly faster in opt builds: TestTXMgr is anywhere from 25-60%
faster (depending on the platform) than when using std::deque from
libstdc++ or libc++.
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