Compiler warning about usage of tmpnam

[falkTX]

Reported by gcc-4.9

/tmp/ccldA0Cc.o: In function `PDLv2Plugin::PDLv2Plugin(double)':
plugin.cpp:(.text._ZN11PDLv2PluginC2Ed[_ZN11PDLv2PluginC5Ed]+0x3aa): warning: the use of `tmpnam' is dangerous, better use `mkstemp'

[x37v]

this is now resolved in the multiinstancelibpd branch, soon to be merged into master.