[PATCH 2.6] fix mmap() return value to conform POSIX

This patch fixes 2 return values in mmap() to conform POSIX spec: [EINVAL] The value of len is zero. [ENOMEM] MAP_FIXED was specified, and the range [addr,addr+len) exceeds that allowed for the address space of a process; or, if MAP_FIXED was not specified

[PATCH 2.6] fix mprotect() with len=(size_t)(-1) to return -ENOMEM

This patch fixes a corner case in sys_mprotect(): Case: len is so large that will overflow to 0 after page alignment. E.g. len=(size_t)(-1), i.e. 0xff...ff. Expected result: POSIX spec says it should return -ENOMEM. Current result: len is aligned to 0, then treated the same as len=0 and return su