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.
CGUI now represents a single 'page'. CGUIManager maintains multiple
pages and switches between them.
Split the XML files into pregame, loading, session and messagebox pages.
Added hotloading of GUI pages.
Minor GUI cleanups.
(Merge from hg 81862d33780c)
This was SVN commit r7214.
