[Pam-developers] Fix for pam_namespace leaking mounts

This is a fix for the problem recently reported in trac. It is not a perfect solution as in case the root user account is polyinstantiated as well it will not be possible to mainpulate the mounts in the parent namespace. However a perfect fix is not possible without changes in kernel mount() syscall implementation and the current problem is much worse. OK to commit? -- Tomas Mraz No matter how far down the wrong road you've gone, turn back. Turkish proverb