Fixed ppid Linux implementation which raised TypeError exception.
Fixed ppid Linux implementation which raised TypeError exception.

anfedorov/psutil,kiranvizru/psutil,huson2012/psutil,chjwang/psutil,huson2012/psutil,end18/psutil,google-code-export/psutil,stupidcache/psutil,nmani1905/psutil,marmolu/psutil,djhaskin987/psutil,end18/psutil,tigerneil/psutil,nmani1905/psutil,jucapj/psutil,skyshe/psutil,end18/psutil,shiva21/psutil,zhengzheng/psutil,Alwnikrotikz/psutil,Alwnikrotikz/psutil,stupidcache/psutil,kiranvizru/psutil,end18/psutil,PFZheng/psutil,vmolsa/psutil,jucapj/psutil,PFZheng/psutil,creativewild/psutil,stupidcache/psutil,vmolsa/psutil,skyshe/psutil,zhengzheng/psutil,vmolsa/psutil,google-code-export/psutil,djhaskin987/psutil,djhaskin987/psutil,skyshe/psutil,AlanZatarain/psutil,skyshe/psutil,creativewild/psutil,vmolsa/psutil,chjwang/psutil,AlanZatarain/psutil,creativewild/psutil,peter-hst/psutil,huson2012/psutil,shiva21/psutil,google-code-export/psutil,djhaskin987/psutil,peter-hst/psutil,tigerneil/psutil,anfedorov/psutil,tigerneil/psutil,kiranvizru/psutil,marmolu/psutil,kiranvizru/psutil,google-code-export/psutil,tigerneil/psutil