version(noboundscheck) + friends

[Ivan Kazmenko]

By the way, what is the naming convention of predefined versions? 
  I am having a hard time trying to figure it out by myself from 
the docs (http://dlang.org/version.html#PredefinedVersions).

To me, it would make sense if all predefined versions started 
with "D_" or something similar to avoid conflicts with user 
versions.  Currently, the exceptions are vendor-related and 
architecture-related (a whole lot of them, actually) as well as 
the following:

unittest
assert
all
none

Now, "all" and "none" are clearly special.  But, really, what's 
the conceptual difference between "unittest", "assert" and 
"D_NoBoundsChecks" which results in using the different naming 
convention?

Ivan Kazmenko.