this bug was fixed shortly before 2.14 release, so we checked for that.
however some distros decided to backport this fix to earlier versions,
breaking our compiletime check.
http://sourceware.org/git/?p=glibc.git;a=commitdiff;h=e4ecafe004b3d4270b3a9dace8f970047400ed38
the portable solution is to stick the function into a separate comilation
unit that does not see the glibc prototype.
closes#7
