Fixed the button index, which became invalid after removing the IOR_BUSY
response in the recent fix of STORM-1543 (changeset 526d86e69101).

STORM-1534: fix credits generation on Windows, adjust to new environment variable convention in build system

reviewed by Stone

EXP-1160 FIX Cannot drag/drop items from inventory into the contents of a prim in latest Mesh build 239475
brought back some old logic for dispatching to child folder as drag and drop fallback

Addressing review feedback.

Fix LLInstanceTracker::key_iter constructor param; accepting
InstanceMap::iterator by non-const reference relied on Microsoft extension
that accepts non-const reference to an rvalue. Given typical iterator
implementation, simply accept by value instead, which makes gcc happy too.