We shouldn't be using MAP_FIXED on solaris (fixes last night's crash).

Unfortunately on Solaris the heuristics don't work too well.  Solaris
seems to ignore the addr argument to mmap when MAP_FIXED is not
specified, and starts handing out memory from the top of the address
space.  So we allocate 2M each time and munmap() ends to leave an
aligned 1M chunk.  This will eventually leave the address space
completely full of 1M holes.  I don't have a good solution to this at
the moment.

MERGE TO STABLE