the old debug_assert always ran and tested the expression, which slows
down release builds. wrapping them in #ifndef NDEBUG is clumsy. the new
ASSERT behaves like assert and ENSURE like the old debug_assert. Let's
change any time-critical but not-super-important ENSURE to ASSERT to
speed up release builds. (already done in bits.h and unique_range.h)
This was SVN commit r9362.
Giant merge from
http://svn.wildfiregames.com/hg-source/file/5fb522019d5e
Infrastructure is largely complete, gameplay is largely missing
Disabled by default; use command-line flag "-sim2"
(Second attempt at commit...)
This was SVN commit r7259.
