large pyroot performance regression in 6.04.10

hi -

I've observed that some calls to C++ from python take 5--10x longer
with root 6.04.10 compared to root 6.02.08. (However, the 6.06
release is much faster than 6.02.08, so this is an issue only
for the 6.04. branch.)

A simple reproducer is attached: it generates a dictionary for a trivial
class method and then calls it multiple times. Execute one of the setup
scripts (such as setup-602, setup-604), then execute the testit script
to build and run the example.

On lxplus, i find that the loop takes about 5 seconds with root 6.02.08
and about 30 seconds with root 6.04.10. (But with root 6.06, it takes
about 1 second.)