CORE-6639 #resolve #time 1d #comment Guard pages now work ;-)

CORE-6639 #resolve #time 1d #comment Guard pages now work ;-)
[NDK]: Fix definition of a global flag.
[RTL]: RtlpCreateUserStack: 1) If the image is invalid, bail out. 2) If the stack commit is higher than reserve, adjust reserve. 3) After allocating a guard page, the stack limit is now ABOVE the guard page, not BELOW it (stack grows backward!).
[RTL]: Remove the hack which always Commited the "StackReserve" value. Threads now have a 4-64KB stack, instead of a 1MB stack.
[NTOSKRNL]: Implement MiAccessCheck and MiCheckForUserStackOverflow, which handle guard page + stack expansion.
[USER32]: Because threads now correctly run with a smaller stack than usual (and expand as needed), remove some checks in user-mode callbacks which forced larger stacks.

svn path=/trunk/; revision=59868