Brought mm0 initialization up to init_execve()

Changes:
It is now possible to use do_mmap() from within mm0.

- pager_new_virtual()/delete_virtual() return addresses that are
  disjoint from find_unmapped_area() used by mmap() interface for
  anonymous or not-fixed areas.
- find_unmapped_area() now uses task->map_start task->map_end instead
  of task->start and task->end. task->start/end are still valid task
  space addresses for mmap(), but finding a new address is limited to
  map_start/map_end.

- We have both interfaces because mmap() is only useful for backed-files.
  When the pager needs to access a user memory range for example, that is
  not backed by a file and thus we need to use pager_new_virtual() instead
  of mmap() for mapping.

src/arch/arm/exception.c

@@ -19,7 +19,7 @@
 #include INC_SUBARCH(mm.h)
 
 /* Abort debugging conditions */
-// #define DEBUG_ABORTS
+ #define DEBUG_ABORTS
 #if defined (DEBUG_ABORTS)
 #define dbg_abort(...)	dprintk(__VA_ARGS__)
 #else