Mixed changes

- Adding prefaulting of fs0 to avoid page fault deadlocks.
- Fixed a bug that a vmo page_cache equivalence would simply drop a link to
  an original vmo, even if the vmo could have more pages outside the page cache,
  or if the vmo was not a shadow vmo.
- Fixed a bug with page allocator where recursion would corrupt global variables.
- Now going to fix or re-write a simpler page allocator that works.

tasks/mm0/include/vm_area.h

@@ -14,7 +14,7 @@
 #include <arch/mm.h>
 #include <lib/spinlock.h>
 
-// #define DEBUG_FAULT_HANDLING
+#define DEBUG_FAULT_HANDLING
 #ifdef DEBUG_FAULT_HANDLING
 #define dprintf(...)	printf(__VA_ARGS__)
 #else