No more xbt_maxmin_float_t not xbt_heap_float_t. I use double everywhere. In

No more xbt_maxmin_float_t not xbt_heap_float_t. I use double everywhere. In
SimGrid 2 I had to use long double for precision reason. Probably because of
the trace integration but I should not need it anymore since there is no
more trace integration. The real question is "is double sufficient for time
values". The answer is yes since for values larger than 272 years, you still
have a precision of 1e-6 s. float is clearly not sufficient however. Let's
use doubles then !

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@620 48e7efb5-ca39-0410-a469-dd3cf9ba447f