Backport PR
#4230: Switch correctly to the user's default matplotlib backend after inline....
Backport PR
#4230: Switch correctly to the user's default matplotlib backend after inline.
If '%matplotlib inline' was called first, we'd incorrectly revert to
inline when plain '%matplotlib' was called, instead of loading the
user's default GUI. If the user called '%matplotlib' first (without
'inline') it worked correctly, but not in the other order.
The fix is to read the backend from the original defaults, not from
the runtime data structure.
