Add an include of stdlib.h to various files that were relying on config.h to drag it in. I don't think config.h should be pulling in standard C headers.
The change mostly consists of removing or replacing non-standard (usually POSIX) header includes.
Guards for replacements for inet_ntop(), inet_pton() and gettimeofday() are updated; the first two are macros on Windows, so the guards are changed to HAVE_DECL. gettimeofday() is present on MinGW builds but not Visual Studio, so that has a function check.