suggested change for cipher/sha1.c's M(i) macro

[Kan Shimizu]

> Please consider using `rol( tm, 1 )' in place of the functionally
> equivalent `(tm << 1) | (tm >> 31)'.

 In my environment, 'rol()' does not exist.
May be, developers need to know on what OS, and with what 
C-compiler, 'rol()' works.

Thanks.
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 Kan Shimizu
 kshimizu at urawa.cabletv.ne.jp
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