regex_replace is not thread safe when format = $N

[r_emek]

When used in a multi-threaded environment,
regex_replace produces wrong results when the 'fmt'
parameter is $<digit> (i.e., $1, $2, etc.). 

If, for example, the correct results of the replacement
operation is 1234, and fmt is '$0', we'll eventually
get one of the following: 
 - 12340
 - $0

(The last digit of the erroneous result is usually the
digit number from the format). 

I'm attaching a sample program that demonstrates the
problem. 

We've seen this problem on Linux (RedHat 9, gcc version
3.2.2 20030222) and on several other platforms. 

[John Maddock]

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This is a duplicate of
https://sourceforge.net/tracker/?func=detail&atid=107586&aid=1530683&group_id=7586.
 See regex-thread.diff for the fix.

John Maddock.

[r_emek]

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Thanks a lot.