Conditional exclusion of header files not present in Windows

Error encountered in MSVS 2010.
Use rand() on Windows

MSVS 2010 reports random() as identifier not found.
Wrap s_catch_signal() in conditional compilation under Windows

MSVS 2010 reports 'sigaction' as unknown identifier.
Merge pull request #348 from negerns/master

Fixes when compiling the MDP protocol example under Windows using MSVS2010