#1 Additional prototypes for improved C99 compatibility

[Florian Weimer]

Future compilers will not support implicit function declarations by default, so compilation will fail without these fixes.

The <grp.h> addition seems to already be included in the current Git sources.

Related to:

• https://fedoraproject.org/wiki/Changes/PortingToModernC
• https://fedoraproject.org/wiki/Toolchain/PortingToModernC