On a Windows debug build the /MT flag was used in addition to
the /MTd flag. Basically harmless except the compiler issued
a warning for every file compiled.
Removed the use of the /MT flag in the jambase arena. This
allows the Jamrules to properly set this flag as required.
Also when doing a Smart Heap debug build, duplicate symbols
in the Smart Heap library conflicted with the standard
Windows CRT library. Adding a /FORCE to the link line solves
this problem. This is a very narrow case and should not effect
builds without Smart Heap.
Jam must be rebuilt to remove the /MT and /MTd warning.