Blender Git Loki

Alembic export: make the start/end frame default values less reasonable

The old default values (start/end frame = 1) could have been an actually
desired setting (for example when exporting a non-animated model). To
make this worse, this was only interpreted as "start/end of the scene" by
the export operator when running interactively, but not when run from
Python.

By choosing INT_MIN as default it's highly unlikely that the interval
[start, end) was intended as actual export range.