[Pam-developers] Fix all warnings encountered with -Wall -Wextra options

The attached patch fixes all warnings encountered in build with -Wall -Wextra options with gcc-9.2.1. I had to suppress two warnings for bison/flex generated code. OK to commit? -- Tomáš Mráz No matter how far down the wrong road you've gone, turn back. Turkish proverb [You'll know whether the road is wrong if you carefully listen to your conscience.]