simplehttpserver: prevent overwriting files outside of document path

Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Jerome.Python2

01:12:52

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:23:57

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:14:41

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:15:21

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:45:38

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:21:10