mgr/ActivePyModule: avoid with_gil where possible

mgr/ActivePyModule: avoid with_gil where possible

The common pattern of

 without_gil_t no_gil;
 ...
 with_gil_t with_gil(no_gil);
 ...

is that when the stack unwindws, ~with_gil_t() will drop the GIL and then
~without_gil_t() will retake it again, adding a completely unnecessary
unlock/lock cycle.

Instead, do

 no_gil.acquire_gil();

when we are ready to retake the GIL.  ~without_gil_t() will then be a
no-op.

Signed-off-by: Sage Weil <sage@newdream.net>