Contrary to xpdf, poppler tries to avoid the use of tmpnam() when mkstemp() is found but mkstemps() is not found [never saw a description of mkstemps]. This results in using mkstemp with an argument "prefixXXXXXX.ext", which will always fail -- at least with GNU libc 2.3.x and 2.4. It seems there is no good way to safely create a temporary file with an extension. Why would one need that. In xpdf and poppler the last argument of openTempFile is always NULL, so this whole thing is broken but unused, i.e., superfluous.
Removed the possibility to specify the extension altogether, will be in poppler 0.12
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