The commit "modified the if command to address bug 9123 some" changed
the if() command behavior with respect to named boolean constants.  It
introduced policy CMP0012 to provide compatibility.  However, it also
changed behavior with respect to numbers (like '2') but did not cover
the change with the policy.  Also, the behavior it created for numbers
is confusing ('2' is false).

This commit teaches if() to recognize numbers again, and treats them
like the C language does in terms of boolean conversion.  We also fix
the CMP0012 check to trigger in all cases where the result of boolean
coersion differs from that produced by CMake 2.6.4.