A few race conditions in the testsuite

[Paolo Carlini]

Hi Howard,

you are analysis and proposed fix make sense, of course. Only, I would 
like to know which is the target showing the problem (x86-darwin?!?), 
thus, be reassured that *on that target* the fix actually works in 
practice (because I cannot do that check anyway: all the targets I have 
available don't show the problem). If you can help me on that, then, I 
can double-check on linux that everything is still fine there, and 
commit the patch. A ChangeLog entry would be also appreciated.

Thanks!
Paolo.