Description:
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The implementation of putenv() in standard/basic_function.c
uses the C library function strtok(). Whilst this is OK when 
compiling with Microsoft Visual C because PHP is linked with 
the Mutithreaded C run-time library (/MD or /MDd option) whether ZTS is enabled or not, the gcc version of strtok() is not thread safe and a separate function strtok_r() is provided should thread safety be required.

Easily resolved without the need for #if def's in code by
changing code to call the php function php_strtok_r() 
as a number of other extensions already do.

Patch to fix the code is here: http://pastebin.ca/256777

Reproduce code:
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Problem found by code inspection. As with most thread safety issues difficult to produce a simple testcase which
will show a reproducible crash but current Linux executable  is clearly not reentrant.

Expected result:
----------------
N/A

Actual result:
--------------
N/A