[Tinyos Core WG] volatiles in scheduler

[John Regehr]

I took a quick look at the volatile variables in SchedulerBasicP and I 
believe that the volatile qualifiers are not needed.

Motivations for removing these would be (1) cleaning up the code (2) 
saving a few bytes of code memory and a few cycles (3) patching a 
bandaid over one of the safe tinyos compiler warnings.

Probably now is not the time but perhaps I'll remove these after 2.1.

Just as a note: ever since David added compiler barriers to 
nesc_atomic_start/end there are only three valid reasons to use volatile 
in TinyOS:

- to prevent the compiler from caching racing variables in registers 
(this is never a problem for non-racing variables)

- accessing HW registers

- (very occasionally) in library code to avoid potential warnings if a 
client of the library passes a volatile-qualified argument

John