Blender Git Loki

Second attempt to fix T40833: Crash when rendering with freestyle.

The cause of the crash was identified in an uninitialized member variable
`Main->lock`. Now that struct Main has a few member variables whose
values are dynamically allocated, per-render Freestyle-specific Main data
structures will be allocated and released using `BKE_main_new()` and
`BKE_main_free()`, respectively.

This revision complements the commit rB6135556f4556.